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Samir Matar

Centre National de la Recherche Scientifique / French National Centre for Scientific Research, ICMCB, Faculty Member

University of Bordeaux (France), CMS, Faculty Member

University of Bordeaux (France), Computational Materials Science, Faculty Member

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I have studied Math, Physcis and Chemistry at the Lebanese University back in 1973-1975, then left to France at 19 because of the war in Lebanon. At the University of Bordeaux I carried on my studies, majoring in Physcial Chemistry (B.Sc/ M.Sc) then went on to Ph.D. venture. From purely experimentalist I turned to computations very early and started modelling properties of fast ionic conductors under the guidance of Professor Richard CATLOW FRS at UCL-London. I learned a lot with Dr Jean-Maurice REAU on fluorides as ionic conductors and he was my supervisor for the two Ph.D.'s (one in Chemistry 1982 and a second -big- one, Doctorat d'Etat in Physical Science Oct.83. I have the honor to have met an benefited from their knowledge great scientisits as Walter KOHN (DFT Nobel prize 1998)

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Skolkovo Institute of Science and Technology

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Chulalongkorn University

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Papers by Samir Matar

Crystal chemistry and ab initio DFT studies of original materials: superhard C5, C4N, and C2N2 nitrides

Academia Materials Science, Mar 3, 2025

Superhard C5 with lon topology (lon: Lonsdaleite hexagonal diamond), characterized by the presenc... more Superhard C5 with lon topology (lon: Lonsdaleite hexagonal diamond), characterized by the presence of sp3 and sp-like carbon sites, is devised from crystal chemistry and used as a template matrix structure for identifying original carbonitrides C4N and C2N2, which also exhibit lon topology, except for the equiatomic belonging to a new topology (3,4L147). The steric effect of N(2s2) lone pair is highlighted in C2N2 through inducing an original structure with a largely separated two-layered stacking of tetrahedra. Such investigations, based on crystal chemistry rationale, were supported by computations within the framework of quantum density functional theory (DFT). All systems were found to be cohesive and both mechanically (elastic constants) and dynamically (phononband structures) stable. Super hardness characterizes the carbon allotrope C5 and the nitrides C4N and C2N2. Metallic-like conductivities and insulating properties were identified, thus offering a range of materials for applications in the field of electronics.

Functional Materials Design through the “Geo-inspired” Concept

Universal Journal of Materials Science

The "Geo-inspired" novel concept is proposed, based on using the crystal and bonding characterist... more The "Geo-inspired" novel concept is proposed, based on using the crystal and bonding characteristics of existing minerals to devise novel man-made materials. It is also used to address grand challenges in designing next generation functional materials such as new ultra-hard materials and layered oxides. Extension is proposed for identifying exotic chemical systems, in order to further stress its generality.

Electron Lone-Pairs Stereochemistry and Drastic van der Waals and Pressure Effects in AsF3 from First Principles

Condensed Matter, 2021

AsF3E as a representative of a molecular crystal has been chosen to find the precise localization... more AsF3E as a representative of a molecular crystal has been chosen to find the precise localization of the lone pair (LP) E centroid 4s2 of As3+ and to enlighten the behavior of lone pair triplets of fluorine atoms. Starting from stereochemistry rationale, Density Functional (DFT) electronic structure calculations yielding the electron localization (ELF) mapping led to precise large crystal structure evolutions from basic X-rays data (V = 267.2Å3 at 193K), to (V = 230.5Å3) and under Van der Waals forces (DEW) V = 206.4Å3, and then under pressure P, all illustrated with ELF maps and band structures. Calibrated pressures up to 100 GPa exhibit the remarkable shrinking of all inter-atomic distances including As-E from 0.94Å down to 0.46Å, while the major three bonds As-F1, As-F2 and As-F3 are continuously expanding. The resulting picture of the application of pressure on AsF3 molecular structure leads to the progressive immersion of the 4s2 doublet within the electronic cloud with an orig...

Joint Stereochemical and ab initio overview of SnII electron lone pairs (E) and F–(E) triplets effects on the crystal networks, the bonding and the electronic structures in a family of tin fluorides

Progress in Solid State Chemistry, 2019

The stereochemistry of 5s 2 (E) lone pair of divalent Sn (Sn II designated by M*) and the lone pa... more The stereochemistry of 5s 2 (E) lone pair of divalent Sn (Sn II designated by M*) and the lone pair triplet around the luorine ions are examined complementarily with stereo-chemical approach and ab initio quantum investigations focusing on the electron localization and pertaining electronic structure properties, obtained within Density Functional Theory (DFT) and derived Electron Localization Function (ELF) mapping. The review completes a series of former ones focusing on the stereochemical role played by electron lone pairs LP. We start by examining LP-free Sn IV F 4 then develop on Sn II F 2 E in its three crystal varieties (α, β, γ). The investigation then extends to study two mixed-valence luorides: Sn 2 II Sn IV F 6 E 2 and Sn II Sn IV F 6 E. The lone pair presence is readily detected in the crystalline network by its sphere of inluence characterized by a radius rE, and M*-E directions; all distances are also detailed and assessed. The observations point to signiicant modiications of the structure which are also analyzed with the electronic density of states DOS projected over the diferent atomic constituents. Within the selected luorides details of Sn II various coordination numbers (CN) generally indicate onesided coordination; speciically: CN = 4 + 1 SnF 4 E triangular bipyramid, CN = 5 + 1 SnF 5 E distorted octahedron (square pyramid with E roughly symmetric of its F apex) and CN = 6 octahedron [SnE]F 6. In the latter, the rotation speed of E (which increases with Z number due to relativistic efects) and the size of the F polyhedron make it favorable enough to E rotating around Sn 2+ with the particularity of its transformation into a large cation [SnE] 2+ with a size comparable to Ca 2+ , Sr 2+ or Ba 2+ .

LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) with ZrNiAl type structure – A systematic view on electronic structure and chemical bonding

Solid State Sciences, 2015

The intermetallic magnesium compounds LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) crystalliz... more The intermetallic magnesium compounds LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) crystallize with the hexagonal ZrNiAl type structure, space group , with full Mg-X ordering. From density functional theory calculations carried out exemplarily on four representative compounds: LaMgX and CeMgX with X = Ga, Pd, significant differences were traced out as to the magnetism arising only for the Ce series leading to identify CeMgGa as an antiferromagnet in its ground state, in agreement with experiment. The bulk module magnitudes show the trend of harder transition metal based ternaries and the cohesive energies favor the X = Pd compounds versus X = Ga ones. Such features were clarified by examining the properties of chemical bonding which exhibit more directional bonds thanks to the Pd d states. Rationalizing the trends of charge transfers, negatively charged triel and transition element atoms are observed. The resulting chemical pictures assign these compounds as gallides and palladides.

n s 2 n p 4 ( n = 4, 5) lone pair triplets whirling in M*F 2 E 3 (M* = Kr, Xe): Stereochemistry and ab initio analyses

Solid State Sciences, 2017

ChemInform Abstract: Different Cerium Valence Transitions Observed by Hydrogenation of the Ternary Germanides CeRhGe and CeIrGe - Structure, Physical Properties and Chemical Bonding

ChemInform, 2008

The ternary germanides CeRhGe and CeIrGe which crystallize in the orthorhombic TiNiSi-type struct... more The ternary germanides CeRhGe and CeIrGe which crystallize in the orthorhombic TiNiSi-type structure, absorb hydrogen at 523 K. X-Ray powder diffraction and transmission electron microscopy indicate that the hydrides CeRhGeH 1.8 and CeIrGeH 1.8 adopt the hexagonal ZrBeSi-type structure. Magnetization, electrical resistivity and thermoelectric power measurements reveal that these hydrides are intermediate-valence compounds. An unusual transition from antiferromagnetic to spin fluctuation behavior occurs upon hydrogenation of CeRhGe, while on the contrary, CeIrGeH 1.8 presents a Kondo temperature of 285 K smaller than that observed for CeIrGe (610 K). In order to explain these opposite valence transitions, the electronic structures of the hydrides have been selfconsistently calculated within the local spin density functional theory (LSDF). The structures are compared to those reported previously by us for CeRhGe and CeIrGe.

Ab-initio Studies of the Electronic Structures of the Hexavalent Uranium Compounds K 2 UO 4 and Na 4 UO 5

Zeitschrift für Naturforschung B, 2014

Band theoretical results within the density functional theory are reported for the uranates K

Segregation of Calcium and Magnesium into Different Substructures. Ca4Ag0.948Mg and Other Compounds with Gd4RhIn-type Structure

Zeitschrift für Naturforschung B, 2012

Yb) were synthesized by induction melting of the elements in sealed tantalum tubes in a water-coo... more Yb) were synthesized by induction melting of the elements in sealed tantalum tubes in a water-cooled sample chamber. All samples were characterized by powder X-ray diffraction. The structures of Ca 4 Ag 0.948 Mg and Yb 4 PdMg were refined on the basis of single-crystal X-ray diffractometer data: Gd 4 RhIn type, F43m, a = 1434.6(1) pm, wR2 = 0.0269, 523 F 2 values, 18 variables for Yb 4 PdMg and a = 1485.78(7) pm, wR2 = 0.0188, 617 F 2 values, 20 variables for Ca 4 Ag 0.948 Mg. For the first time small defects on the 16e transition metal site of a Gd 4 RhIn-type compound have been observed, and the first compounds of this structure type with the divalent rare earth elements europium and ytterbium as well as with calcium are reported. The striking structural motif of these compounds (exemplary for Ca 4 Ag 0.948 Mg) is the clear segregation of two alkaline earth elements into two different substructures, calcium forming trigonal prisms around the silver atoms and magnesium forming covalently bonded tetrahedra (Mg-Mg 328 pm). The latter are embedded in larger cavities of the adamantane-like three-dimensional network of edge-and corner-sharing AgCa 6 trigonal prisms. This is evident from the chemical bonding analysis of the electronic structure by ab initio calculations. The density of states shows s-like metallic conductivity with an active role played by the Ag d states within the valence band and for the bonding with calcium. Temperature-dependent magnetic susceptibility data of Eu 4 PdMg and Eu 4 PtMg show Curie-Weiss behavior above 230 K with experimental magnetic moments of 7.94(1) and 8.00(1) µ B per Eu atom for the palladium and platinum compound, respectively. Ferromagnetic ordering is detected at the comparatively high Curie temperatures of 150.1(5) (Eu 4 PdMg) and 139.1(5) (Eu 4 PtMg) K. Magnetization measurements at 3 K show full parallel spin alignment and the typical behavior of soft ferromagnets.

SrAu4.76In1.24 with YbMo2Al4-type Structure

Zeitschrift für Naturforschung B, 2011

The gold-rich intermetallic compound SrAu 4.76 In 1.24 was synthesized by high-frequence-melting ... more The gold-rich intermetallic compound SrAu 4.76 In 1.24 was synthesized by high-frequence-melting of the elements in a sealed tantalum tube and subsequent annealing. The structure was refined from single-crystal X-ray diffraction data: YbMo 2 Al 4-type, I4/mmm, Z = 2, a = 718.77(7), c = 552.79(9) pm, wR2 = 0.0760, 149 F 2 values and 11 parameters. The 4d (0.62 In + 0.38 Au) Wyckoff position shows mixed occupancy leading to the composition SrAu 4.76 In 1.24 for the investigated crystal. The strontium atoms are located in a large cage built up by 12 Au + 8 In atoms. The gold and indium atoms show segregation into substructures. The striking structural motifs are Au 4 squares (278 pm Au-Au) and indium chains (276 pm In-In). The squares and chains are connected via weaker Au-Au (299 pm) and Au-In (295 pm) bonds to a three-dimensional network. The In chains show the motif of rod packing. Electronic structure calculations show anisotropy within the structure with different responses to compressions along In-In chains and Au planes, also illustrated by the electron localization contour plots. The metallic behavior is found to be of itinerant electron type (like Cu), and the chemical bonding includes stabilizing Au-In interactions.

Ca T Mg 2 and Ca T Cd 2 ( T  = Rh, Pd, Pt) with YPd 2 Si-type Structure

Zeitschrift für Naturforschung B, 2013

The intermetallic calcium compounds CaT Mg 2 and CaT Cd 2 (T = Rh, Pd, Pt) were obtained by high-... more The intermetallic calcium compounds CaT Mg 2 and CaT Cd 2 (T = Rh, Pd, Pt) were obtained by high-frequency melting of the elements in sealed niobium ampoules or through reactions in muffle furnaces. The polycrystalline samples were characterized by powder X-ray diffraction. They crystallize with a site occupancy variant of YPd 2 Si, a ternary ordered version of Fe 3 C. The structures of CaPdMg 2 and CaPdCd 2 were refined from single-crystal diffractometer data: Pnma, a = 792.2(2), b = 803.4(2), c = 572.0(1) pm, wR2 = 0.0663, 1621 F 2 values, 24 variables for Ca 0.94 PdMg 2.06 and a = 794.6(2), b = 809.5(3), c = 554.7(2) pm, wR2 = 0.0301, 819 F 2 values, 23 variables for CaPdCd 2. A small range of homogeneity was observed for Ca 1−x PdMg 2+x. The magnesium and cadmium atoms build up three-dimensional tetrahedral substructures (306-327 pm Mg-Mg and 307-317 pm Cd-Cd) that resemble hexagonal diamond, lonsdaleite. Together with the palladium atoms one obtains three-dimensional, covalently bonded [PdMg 2 ] and [PdCd 2 ] networks which leave cages for the calcium atoms. The latter are bonded to these networks via shorter Ca-Pd contacts (298-319 pm in Ca 0.94 PdMg 2.06 and 295-312 pm in CaPdCd 2). The course of the interatomic distances is in line with calculated overlap populations. The CaPdMg 2 , SrPdMg 2 and CaRhIn 2 structures are all derived from a CaIn 2-related subcell by an ordered filling of transition metal atoms into trigonal prisms. This leads to different herringbone patterns for the networks of puckered and elongated hexagons of magnesium and indium atoms.

First principles investigations of the hydrogenation effects on the electronic structure and the chemical bonding of CeIrAl

Solid State Sciences, 2011

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy First principles investigations of the hydrogenation effects on the electronic structure and the chemical bonding of CeIrAl

Ab initio investigations of the Ca2IrO4-type structure as a “post-K2NiF4”: Case study of Na2OsO4

Solid State Sciences, 2011

Deriving the energyevolume equation of state for Na 2 OsO 4 in its actual Ca 2 IrO 4-type structu... more Deriving the energyevolume equation of state for Na 2 OsO 4 in its actual Ca 2 IrO 4-type structure at high pressure and in hypothetic K 2 NiF 4-type, leads to energy destabilization at a larger volume for the latter and to propose the former as a post-K 2 NiF 4 through which a tuning of the magnetism and conductivity can be achieved: while the oxide system is magnetically silent in Ca 2 IrO 4-type due to spin pairing (S ¼ 0 for d 2 Os 6þ) with a semi-conducting behavior, a finite moment develops in the latter when spin polarization is accounted for (S ¼ 1).

Effect of H insertion on the magnetic, electronic, and structural properties of CeCoSi

Physical Review B, 2004

Contrary to other cerium equiatomic intermetallic systems (CeTX with T = transition metal, X = p ... more Contrary to other cerium equiatomic intermetallic systems (CeTX with T = transition metal, X = p metal) which become magnetically ordered upon hydrogen insertion, magnetic measurements characterize an antiferromagnet for CeCoSi and a spin fluctuation system for its hydride CeCoSiH. The presented results of electrical and magnetic properties of the silicide CeCoSi demonstrate the existence of an antiferromagnetic transition at T N = 8.8͑2͒ K. For the purpose of further assessing the experimental findings, the electronic and magnetic sructures of CeCoSi and CeCoSiH are self-consistently calculated within the local spin density functional LSDF theory. The analysis of the electronic structures and of the chemical bonding properties lead to suggest that the chemical effect of hydrogen prevails over the cell expansion effect which would enhance the magnetization otherwise. Spin orbit coupling effects on cerium are examined. A potential antiferromagnetic structure with a propagation along the c axis is proposed for CeCoSi ground state.

Ab initio investigation of the electronic structure of CeRh2Sb2

Chemical Physics Letters, 2012

ABSTRACT

YNi and its hydrides: Phase stabilities, electronic structures and chemical bonding properties from first principles

Chemical Physics, 2010

Within density functional theory, establishing the equations of states of YNi in two different co... more Within density functional theory, establishing the equations of states of YNi in two different controversial structures in the literature, leads to determine the orthorhombic FeB-type as the ground state one with small energy difference. For YNiH 3 and YNiH 4 hydrides crystallizing in the orthorhombic CrB-type structure the geometry optimization and the ab initio determination of the H atomic positions show that the stability of hydrogen decreases from the tri-to the tetra-hydride. New states brought by hydrogen within the valence band lead to its broadening and to enhanced localization of metal density of states. The chemical bonding analysis shows a preferential Ni-H bonding versus Y-H.

Ab initio investigation of perovskite and post-perovskite CaPtO3

Chemical Physics, 2008

For the recently synthesized post-perovskite (PPV) CaPtO 3 we investigate the electronic band str... more For the recently synthesized post-perovskite (PPV) CaPtO 3 we investigate the electronic band structure properties in connection with hypothetical perovskite PV-CaPtO 3 within density functional theory using pseudopotential and all electron methods. Both systems are found insulating in agreement with a tetravalent Pt(IV) low spin d 6 state. The equilibrium values of the volume and energy point to a stabilization of the PPV versus PV oxide with a smaller volume in agreement with other homologue systems within Earth lower mantle such as PPV-MgSiO 3. This is also addressed from the analysis of the chemical bonding focusing on the change of the Pt-O bonding upon going from PV and PPV systems whereby the covalent Pt-O bonds are differentiated and reinforced within PPV system with respect to PV.

First principles studies of SnTiO3 perovskite as potential environmentally benign ferroelectric material

Chemical Physics, 2009

In the context of the search for environment-respectful, lead-and bismuth-free chemical compounds... more In the context of the search for environment-respectful, lead-and bismuth-free chemical compounds for devices such as actuators, SnTiO 3 (ST) is investigated from first principles within DFT. Full geometry optimization provides a stable tetragonal structure relative to cubic one. From the equation of state the equilibrium volume of SnTiO 3 is found smaller than ferroelectric PbTiO 3 (PT) in agreement with a smaller Sn 2+ radius. While ionic displacements exhibit similar trends between ST and PT, a larger tetragonality (c/a ratio) for ST results in a larger polarization, P ST = 1.1 Cm À2. Within ST analyzes of site projected density of states and chemical bonding indicate a reinforcement of the bond covalence with respect to Pb homologue. Both PT and ST exhibit anomalous large effective charges and the dielectric constant of ST is calculated larger than PT.

Potential existence of anti-postperovskite iron nitride Fe4N

Solid State Sciences, 2010

The equations of state for cubic anti-perovskite (APV) and hypothetic anti post-perovskite (APPV)... more The equations of state for cubic anti-perovskite (APV) and hypothetic anti post-perovskite (APPV) forms of Fe 4 N obtained within DFT for the spin polarized and non-magnetic configurations, confirm the ferromagnetic ground state of APV-Fe 4 N and a non-magnetic one for APPV. The lower equilibrium volume for the latter favors pressure-enabled transition: APV/APPV. Chemical bonding analysis accounting for Fe differentiation into three sublattices for APPV characterized by edge and corner sharing octahedra, leads to a reinforced FeeN chemical bonding. This is argued to help triggering the pressure transformation. It is the first case of potential post-anti-perovskite nitride.

New Journal of Physics First principles study of the electronic and magnetic structures of U 2 Ni 2 SnH 2

New Journal of Physics

The electronic and magnetic properties and the chemical bonding in recently evidenced U 2 Ni 2 Sn... more The electronic and magnetic properties and the chemical bonding in recently evidenced U 2 Ni 2 SnH 2 are self-consistently calculated within the local spin density-functional (LSDF) theory using the scalar-relativistic augmented spherical wave (ASW) method. Trends of the magnetism are discussed in terms of the changes brought by hydrogen within the pure U 2 Ni 2 Sn alloy system from both the volume expansion simulating negative pressure and the bonding between H and lattice constituents U, Ni and Sn pointing to a larger Ni–H bonding versus U–H. The ground state is found to be antiferromagnetic in agreement with experiment. Considering the relativistic effects of spin–orbit coupling an ordered magnetic moment, m U = 1 µ B is calculated for U(5f), close to the experimental magnitude of m U = 0.83 µ B .

Crystal chemistry and ab initio DFT studies of original materials: superhard C5, C4N, and C2N2 nitrides

Academia Materials Science, Mar 3, 2025

Superhard C5 with lon topology (lon: Lonsdaleite hexagonal diamond), characterized by the presenc... more Superhard C5 with lon topology (lon: Lonsdaleite hexagonal diamond), characterized by the presence of sp3 and sp-like carbon sites, is devised from crystal chemistry and used as a template matrix structure for identifying original carbonitrides C4N and C2N2, which also exhibit lon topology, except for the equiatomic belonging to a new topology (3,4L147). The steric effect of N(2s2) lone pair is highlighted in C2N2 through inducing an original structure with a largely separated two-layered stacking of tetrahedra. Such investigations, based on crystal chemistry rationale, were supported by computations within the framework of quantum density functional theory (DFT). All systems were found to be cohesive and both mechanically (elastic constants) and dynamically (phononband structures) stable. Super hardness characterizes the carbon allotrope C5 and the nitrides C4N and C2N2. Metallic-like conductivities and insulating properties were identified, thus offering a range of materials for applications in the field of electronics.

Functional Materials Design through the “Geo-inspired” Concept

Universal Journal of Materials Science

The "Geo-inspired" novel concept is proposed, based on using the crystal and bonding characterist... more The "Geo-inspired" novel concept is proposed, based on using the crystal and bonding characteristics of existing minerals to devise novel man-made materials. It is also used to address grand challenges in designing next generation functional materials such as new ultra-hard materials and layered oxides. Extension is proposed for identifying exotic chemical systems, in order to further stress its generality.

Electron Lone-Pairs Stereochemistry and Drastic van der Waals and Pressure Effects in AsF3 from First Principles

Condensed Matter, 2021

AsF3E as a representative of a molecular crystal has been chosen to find the precise localization... more AsF3E as a representative of a molecular crystal has been chosen to find the precise localization of the lone pair (LP) E centroid 4s2 of As3+ and to enlighten the behavior of lone pair triplets of fluorine atoms. Starting from stereochemistry rationale, Density Functional (DFT) electronic structure calculations yielding the electron localization (ELF) mapping led to precise large crystal structure evolutions from basic X-rays data (V = 267.2Å3 at 193K), to (V = 230.5Å3) and under Van der Waals forces (DEW) V = 206.4Å3, and then under pressure P, all illustrated with ELF maps and band structures. Calibrated pressures up to 100 GPa exhibit the remarkable shrinking of all inter-atomic distances including As-E from 0.94Å down to 0.46Å, while the major three bonds As-F1, As-F2 and As-F3 are continuously expanding. The resulting picture of the application of pressure on AsF3 molecular structure leads to the progressive immersion of the 4s2 doublet within the electronic cloud with an orig...

Joint Stereochemical and ab initio overview of SnII electron lone pairs (E) and F–(E) triplets effects on the crystal networks, the bonding and the electronic structures in a family of tin fluorides

Progress in Solid State Chemistry, 2019

The stereochemistry of 5s 2 (E) lone pair of divalent Sn (Sn II designated by M*) and the lone pa... more The stereochemistry of 5s 2 (E) lone pair of divalent Sn (Sn II designated by M*) and the lone pair triplet around the luorine ions are examined complementarily with stereo-chemical approach and ab initio quantum investigations focusing on the electron localization and pertaining electronic structure properties, obtained within Density Functional Theory (DFT) and derived Electron Localization Function (ELF) mapping. The review completes a series of former ones focusing on the stereochemical role played by electron lone pairs LP. We start by examining LP-free Sn IV F 4 then develop on Sn II F 2 E in its three crystal varieties (α, β, γ). The investigation then extends to study two mixed-valence luorides: Sn 2 II Sn IV F 6 E 2 and Sn II Sn IV F 6 E. The lone pair presence is readily detected in the crystalline network by its sphere of inluence characterized by a radius rE, and M*-E directions; all distances are also detailed and assessed. The observations point to signiicant modiications of the structure which are also analyzed with the electronic density of states DOS projected over the diferent atomic constituents. Within the selected luorides details of Sn II various coordination numbers (CN) generally indicate onesided coordination; speciically: CN = 4 + 1 SnF 4 E triangular bipyramid, CN = 5 + 1 SnF 5 E distorted octahedron (square pyramid with E roughly symmetric of its F apex) and CN = 6 octahedron [SnE]F 6. In the latter, the rotation speed of E (which increases with Z number due to relativistic efects) and the size of the F polyhedron make it favorable enough to E rotating around Sn 2+ with the particularity of its transformation into a large cation [SnE] 2+ with a size comparable to Ca 2+ , Sr 2+ or Ba 2+ .

LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) with ZrNiAl type structure – A systematic view on electronic structure and chemical bonding

Solid State Sciences, 2015

The intermetallic magnesium compounds LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) crystalliz... more The intermetallic magnesium compounds LaMgX and CeMgX (X = Ga, In, Tl, Pd, Ag, Pt, Au) crystallize with the hexagonal ZrNiAl type structure, space group , with full Mg-X ordering. From density functional theory calculations carried out exemplarily on four representative compounds: LaMgX and CeMgX with X = Ga, Pd, significant differences were traced out as to the magnetism arising only for the Ce series leading to identify CeMgGa as an antiferromagnet in its ground state, in agreement with experiment. The bulk module magnitudes show the trend of harder transition metal based ternaries and the cohesive energies favor the X = Pd compounds versus X = Ga ones. Such features were clarified by examining the properties of chemical bonding which exhibit more directional bonds thanks to the Pd d states. Rationalizing the trends of charge transfers, negatively charged triel and transition element atoms are observed. The resulting chemical pictures assign these compounds as gallides and palladides.

n s 2 n p 4 ( n = 4, 5) lone pair triplets whirling in M*F 2 E 3 (M* = Kr, Xe): Stereochemistry and ab initio analyses

Solid State Sciences, 2017

ChemInform Abstract: Different Cerium Valence Transitions Observed by Hydrogenation of the Ternary Germanides CeRhGe and CeIrGe - Structure, Physical Properties and Chemical Bonding

ChemInform, 2008

The ternary germanides CeRhGe and CeIrGe which crystallize in the orthorhombic TiNiSi-type struct... more The ternary germanides CeRhGe and CeIrGe which crystallize in the orthorhombic TiNiSi-type structure, absorb hydrogen at 523 K. X-Ray powder diffraction and transmission electron microscopy indicate that the hydrides CeRhGeH 1.8 and CeIrGeH 1.8 adopt the hexagonal ZrBeSi-type structure. Magnetization, electrical resistivity and thermoelectric power measurements reveal that these hydrides are intermediate-valence compounds. An unusual transition from antiferromagnetic to spin fluctuation behavior occurs upon hydrogenation of CeRhGe, while on the contrary, CeIrGeH 1.8 presents a Kondo temperature of 285 K smaller than that observed for CeIrGe (610 K). In order to explain these opposite valence transitions, the electronic structures of the hydrides have been selfconsistently calculated within the local spin density functional theory (LSDF). The structures are compared to those reported previously by us for CeRhGe and CeIrGe.

Ab-initio Studies of the Electronic Structures of the Hexavalent Uranium Compounds K 2 UO 4 and Na 4 UO 5

Zeitschrift für Naturforschung B, 2014

Band theoretical results within the density functional theory are reported for the uranates K

Segregation of Calcium and Magnesium into Different Substructures. Ca4Ag0.948Mg and Other Compounds with Gd4RhIn-type Structure

Zeitschrift für Naturforschung B, 2012

Yb) were synthesized by induction melting of the elements in sealed tantalum tubes in a water-coo... more Yb) were synthesized by induction melting of the elements in sealed tantalum tubes in a water-cooled sample chamber. All samples were characterized by powder X-ray diffraction. The structures of Ca 4 Ag 0.948 Mg and Yb 4 PdMg were refined on the basis of single-crystal X-ray diffractometer data: Gd 4 RhIn type, F43m, a = 1434.6(1) pm, wR2 = 0.0269, 523 F 2 values, 18 variables for Yb 4 PdMg and a = 1485.78(7) pm, wR2 = 0.0188, 617 F 2 values, 20 variables for Ca 4 Ag 0.948 Mg. For the first time small defects on the 16e transition metal site of a Gd 4 RhIn-type compound have been observed, and the first compounds of this structure type with the divalent rare earth elements europium and ytterbium as well as with calcium are reported. The striking structural motif of these compounds (exemplary for Ca 4 Ag 0.948 Mg) is the clear segregation of two alkaline earth elements into two different substructures, calcium forming trigonal prisms around the silver atoms and magnesium forming covalently bonded tetrahedra (Mg-Mg 328 pm). The latter are embedded in larger cavities of the adamantane-like three-dimensional network of edge-and corner-sharing AgCa 6 trigonal prisms. This is evident from the chemical bonding analysis of the electronic structure by ab initio calculations. The density of states shows s-like metallic conductivity with an active role played by the Ag d states within the valence band and for the bonding with calcium. Temperature-dependent magnetic susceptibility data of Eu 4 PdMg and Eu 4 PtMg show Curie-Weiss behavior above 230 K with experimental magnetic moments of 7.94(1) and 8.00(1) µ B per Eu atom for the palladium and platinum compound, respectively. Ferromagnetic ordering is detected at the comparatively high Curie temperatures of 150.1(5) (Eu 4 PdMg) and 139.1(5) (Eu 4 PtMg) K. Magnetization measurements at 3 K show full parallel spin alignment and the typical behavior of soft ferromagnets.

SrAu4.76In1.24 with YbMo2Al4-type Structure

Zeitschrift für Naturforschung B, 2011

The gold-rich intermetallic compound SrAu 4.76 In 1.24 was synthesized by high-frequence-melting ... more The gold-rich intermetallic compound SrAu 4.76 In 1.24 was synthesized by high-frequence-melting of the elements in a sealed tantalum tube and subsequent annealing. The structure was refined from single-crystal X-ray diffraction data: YbMo 2 Al 4-type, I4/mmm, Z = 2, a = 718.77(7), c = 552.79(9) pm, wR2 = 0.0760, 149 F 2 values and 11 parameters. The 4d (0.62 In + 0.38 Au) Wyckoff position shows mixed occupancy leading to the composition SrAu 4.76 In 1.24 for the investigated crystal. The strontium atoms are located in a large cage built up by 12 Au + 8 In atoms. The gold and indium atoms show segregation into substructures. The striking structural motifs are Au 4 squares (278 pm Au-Au) and indium chains (276 pm In-In). The squares and chains are connected via weaker Au-Au (299 pm) and Au-In (295 pm) bonds to a three-dimensional network. The In chains show the motif of rod packing. Electronic structure calculations show anisotropy within the structure with different responses to compressions along In-In chains and Au planes, also illustrated by the electron localization contour plots. The metallic behavior is found to be of itinerant electron type (like Cu), and the chemical bonding includes stabilizing Au-In interactions.

Ca T Mg 2 and Ca T Cd 2 ( T  = Rh, Pd, Pt) with YPd 2 Si-type Structure

Zeitschrift für Naturforschung B, 2013

The intermetallic calcium compounds CaT Mg 2 and CaT Cd 2 (T = Rh, Pd, Pt) were obtained by high-... more The intermetallic calcium compounds CaT Mg 2 and CaT Cd 2 (T = Rh, Pd, Pt) were obtained by high-frequency melting of the elements in sealed niobium ampoules or through reactions in muffle furnaces. The polycrystalline samples were characterized by powder X-ray diffraction. They crystallize with a site occupancy variant of YPd 2 Si, a ternary ordered version of Fe 3 C. The structures of CaPdMg 2 and CaPdCd 2 were refined from single-crystal diffractometer data: Pnma, a = 792.2(2), b = 803.4(2), c = 572.0(1) pm, wR2 = 0.0663, 1621 F 2 values, 24 variables for Ca 0.94 PdMg 2.06 and a = 794.6(2), b = 809.5(3), c = 554.7(2) pm, wR2 = 0.0301, 819 F 2 values, 23 variables for CaPdCd 2. A small range of homogeneity was observed for Ca 1−x PdMg 2+x. The magnesium and cadmium atoms build up three-dimensional tetrahedral substructures (306-327 pm Mg-Mg and 307-317 pm Cd-Cd) that resemble hexagonal diamond, lonsdaleite. Together with the palladium atoms one obtains three-dimensional, covalently bonded [PdMg 2 ] and [PdCd 2 ] networks which leave cages for the calcium atoms. The latter are bonded to these networks via shorter Ca-Pd contacts (298-319 pm in Ca 0.94 PdMg 2.06 and 295-312 pm in CaPdCd 2). The course of the interatomic distances is in line with calculated overlap populations. The CaPdMg 2 , SrPdMg 2 and CaRhIn 2 structures are all derived from a CaIn 2-related subcell by an ordered filling of transition metal atoms into trigonal prisms. This leads to different herringbone patterns for the networks of puckered and elongated hexagons of magnesium and indium atoms.

First principles investigations of the hydrogenation effects on the electronic structure and the chemical bonding of CeIrAl

Solid State Sciences, 2011

This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy First principles investigations of the hydrogenation effects on the electronic structure and the chemical bonding of CeIrAl

Ab initio investigations of the Ca2IrO4-type structure as a “post-K2NiF4”: Case study of Na2OsO4

Solid State Sciences, 2011

Deriving the energyevolume equation of state for Na 2 OsO 4 in its actual Ca 2 IrO 4-type structu... more Deriving the energyevolume equation of state for Na 2 OsO 4 in its actual Ca 2 IrO 4-type structure at high pressure and in hypothetic K 2 NiF 4-type, leads to energy destabilization at a larger volume for the latter and to propose the former as a post-K 2 NiF 4 through which a tuning of the magnetism and conductivity can be achieved: while the oxide system is magnetically silent in Ca 2 IrO 4-type due to spin pairing (S ¼ 0 for d 2 Os 6þ) with a semi-conducting behavior, a finite moment develops in the latter when spin polarization is accounted for (S ¼ 1).

Effect of H insertion on the magnetic, electronic, and structural properties of CeCoSi

Physical Review B, 2004

Contrary to other cerium equiatomic intermetallic systems (CeTX with T = transition metal, X = p ... more Contrary to other cerium equiatomic intermetallic systems (CeTX with T = transition metal, X = p metal) which become magnetically ordered upon hydrogen insertion, magnetic measurements characterize an antiferromagnet for CeCoSi and a spin fluctuation system for its hydride CeCoSiH. The presented results of electrical and magnetic properties of the silicide CeCoSi demonstrate the existence of an antiferromagnetic transition at T N = 8.8͑2͒ K. For the purpose of further assessing the experimental findings, the electronic and magnetic sructures of CeCoSi and CeCoSiH are self-consistently calculated within the local spin density functional LSDF theory. The analysis of the electronic structures and of the chemical bonding properties lead to suggest that the chemical effect of hydrogen prevails over the cell expansion effect which would enhance the magnetization otherwise. Spin orbit coupling effects on cerium are examined. A potential antiferromagnetic structure with a propagation along the c axis is proposed for CeCoSi ground state.

Ab initio investigation of the electronic structure of CeRh2Sb2

Chemical Physics Letters, 2012

ABSTRACT

YNi and its hydrides: Phase stabilities, electronic structures and chemical bonding properties from first principles

Chemical Physics, 2010

Within density functional theory, establishing the equations of states of YNi in two different co... more Within density functional theory, establishing the equations of states of YNi in two different controversial structures in the literature, leads to determine the orthorhombic FeB-type as the ground state one with small energy difference. For YNiH 3 and YNiH 4 hydrides crystallizing in the orthorhombic CrB-type structure the geometry optimization and the ab initio determination of the H atomic positions show that the stability of hydrogen decreases from the tri-to the tetra-hydride. New states brought by hydrogen within the valence band lead to its broadening and to enhanced localization of metal density of states. The chemical bonding analysis shows a preferential Ni-H bonding versus Y-H.

Ab initio investigation of perovskite and post-perovskite CaPtO3

Chemical Physics, 2008

For the recently synthesized post-perovskite (PPV) CaPtO 3 we investigate the electronic band str... more For the recently synthesized post-perovskite (PPV) CaPtO 3 we investigate the electronic band structure properties in connection with hypothetical perovskite PV-CaPtO 3 within density functional theory using pseudopotential and all electron methods. Both systems are found insulating in agreement with a tetravalent Pt(IV) low spin d 6 state. The equilibrium values of the volume and energy point to a stabilization of the PPV versus PV oxide with a smaller volume in agreement with other homologue systems within Earth lower mantle such as PPV-MgSiO 3. This is also addressed from the analysis of the chemical bonding focusing on the change of the Pt-O bonding upon going from PV and PPV systems whereby the covalent Pt-O bonds are differentiated and reinforced within PPV system with respect to PV.

First principles studies of SnTiO3 perovskite as potential environmentally benign ferroelectric material

Chemical Physics, 2009

In the context of the search for environment-respectful, lead-and bismuth-free chemical compounds... more In the context of the search for environment-respectful, lead-and bismuth-free chemical compounds for devices such as actuators, SnTiO 3 (ST) is investigated from first principles within DFT. Full geometry optimization provides a stable tetragonal structure relative to cubic one. From the equation of state the equilibrium volume of SnTiO 3 is found smaller than ferroelectric PbTiO 3 (PT) in agreement with a smaller Sn 2+ radius. While ionic displacements exhibit similar trends between ST and PT, a larger tetragonality (c/a ratio) for ST results in a larger polarization, P ST = 1.1 Cm À2. Within ST analyzes of site projected density of states and chemical bonding indicate a reinforcement of the bond covalence with respect to Pb homologue. Both PT and ST exhibit anomalous large effective charges and the dielectric constant of ST is calculated larger than PT.

Potential existence of anti-postperovskite iron nitride Fe4N

Solid State Sciences, 2010

The equations of state for cubic anti-perovskite (APV) and hypothetic anti post-perovskite (APPV)... more The equations of state for cubic anti-perovskite (APV) and hypothetic anti post-perovskite (APPV) forms of Fe 4 N obtained within DFT for the spin polarized and non-magnetic configurations, confirm the ferromagnetic ground state of APV-Fe 4 N and a non-magnetic one for APPV. The lower equilibrium volume for the latter favors pressure-enabled transition: APV/APPV. Chemical bonding analysis accounting for Fe differentiation into three sublattices for APPV characterized by edge and corner sharing octahedra, leads to a reinforced FeeN chemical bonding. This is argued to help triggering the pressure transformation. It is the first case of potential post-anti-perovskite nitride.

New Journal of Physics First principles study of the electronic and magnetic structures of U 2 Ni 2 SnH 2

New Journal of Physics

The electronic and magnetic properties and the chemical bonding in recently evidenced U 2 Ni 2 Sn... more The electronic and magnetic properties and the chemical bonding in recently evidenced U 2 Ni 2 SnH 2 are self-consistently calculated within the local spin density-functional (LSDF) theory using the scalar-relativistic augmented spherical wave (ASW) method. Trends of the magnetism are discussed in terms of the changes brought by hydrogen within the pure U 2 Ni 2 Sn alloy system from both the volume expansion simulating negative pressure and the bonding between H and lattice constituents U, Ni and Sn pointing to a larger Ni–H bonding versus U–H. The ground state is found to be antiferromagnetic in agreement with experiment. Considering the relativistic effects of spin–orbit coupling an ordered magnetic moment, m U = 1 µ B is calculated for U(5f), close to the experimental magnitude of m U = 0.83 µ B .