Papers by Michel Van Hove
Diffraction, in light optics, has been defined as “Any departure of the actual light path from th... more Diffraction, in light optics, has been defined as “Any departure of the actual light path from that prescribed by geometrical optics” [1]. Contrary to light, where the discovery of diffraction preceded the wave theory, electron diffraction was discovered as a consequence of a deliberate attempt to prove the wave nature of the electron. In 1924 Louis de Broglie advanced the, for the times, revolutionary view that electrons (or any corpuscles) are accompanied by waves [2). The origins of that view can be traced back to Einstein’s 1905 theory about the wave– particle duality of light. Starting with this theory of Einstein, de Broglie came to the conclusion that electrons should exhibit the same kind of dual nature as light, where the relation between a particle’s mass m0, its velocity v, and its wavelength λ could be expressed as
Diffraction, in light optics, has been defined as “Any departure of the actual light path from th... more Diffraction, in light optics, has been defined as “Any departure of the actual light path from that prescribed by geometrical optics” [1]. Contrary to light, where the discovery of diffraction preceded the wave theory, electron diffraction was discovered as a consequence of a deliberate attempt to prove the wave nature of the electron. In 1924 Louis de Broglie advanced the, for the times, revolutionary view that electrons (or any corpuscles) are accompanied by waves [2). The origins of that view can be traced back to Einstein’s 1905 theory about the wave– particle duality of light. Starting with this theory of Einstein, de Broglie came to the conclusion that electrons should exhibit the same kind of dual nature as light, where the relation between a particle’s mass m0, its velocity v, and its wavelength λ could be expressed as
Advances in Quantum Chemistry Volume 20
2 3.1. General Four-Step Description of Electron-Diffraction Techniques 3.2. 3.3. 3.4. Structural... more 2 3.1. General Four-Step Description of Electron-Diffraction Techniques 3.2. 3.3. 3.4. Structural Information Theoretical Aspects of Individual Techniques Formalism for Individual Processes 3.5. Unifying and Distinguishing Features 4. THE THEORY OF SURF ACE CHEMISTRY AND BONDING 4.1. The Extended Hi.ickel Theory and Applications 4.2. The SCF Xa Scattered Wave Method 4.3. SCF-Xa-SW Calculations 4.4. Results of the Xa-Method 4.5. The Hartree-Fock-Slater Method and Its Applications 4.6. The ab initio Quantum Chemical Calculation 4.7. • Conclusion 5. •
The Journal of Physical Chemistry B
Artificial molecular machines have played an indispensable role in many chemical and biological p... more Artificial molecular machines have played an indispensable role in many chemical and biological processes in recent decades. Among all kinds of molecular machines, molecular rotor systems have attracted increasing attention. In this work, we used density functional theory (DFT) calculations to investigate the rotational behaviors of on-surface molecular rotors based on porphyrin, which is a species of molecule with wide biological and chemical compatibilities. Moreover, our comparative studies demonstrate that macrocycle metalation, replacing the supporting substrate and substituting functional groups can effectively modify the rotational barrier of porphyrin rotors. We believe that these modification methods can further guide the path to achieve highly controllable on-surface molecular rotor systems in future applications.
The Journal of Physical Chemistry Letters
ACS Nano
While molecular machines play an increasingly significant role in nanoscience research and applic... more While molecular machines play an increasingly significant role in nanoscience research and applications, there remains a shortage of investigations and understanding of the molecular gear (cogwheel), which is an indispensable and fundamental component to drive a larger correlated molecular machine system. Employing ab initio calculations, we investigate model systems consisting of molecules adsorbed on metal or graphene surfaces, ranging from very simple triplearm gears such as PF3 and NH3 to larger multi-arm gears based on carbon rings. We explore in detail the transmission of slow rotational motion from one gear to the next by these relatively simple molecules, so as to isolate and reveal the mechanisms of the relevant intermolecular interactions. Several characteristics of molecular gears are discussed, in particular the flexibility of the arms and the slipping and skipping between interlocking arms of adjacent gears, which differ from familiar macroscopic rigid gears. The underlying theoretical concepts suggest strongly that other analogous structures may also exhibit similar behavior which may inspire future exploration in designing large correlated molecular machines.
Surface Science
Abstract We report an unusual self-assembled layer structure of chloroaluminium phthalocyanine (C... more Abstract We report an unusual self-assembled layer structure of chloroaluminium phthalocyanine (ClAlPc) molecules on highly ordered pyrolytic graphite (HOPG), in which a close-packed well-ordered monolayer is separated from the substrate by a relatively disordered buffer layer, as revealed using scanning tunneling microscopy (STM). Our close-packed monolayer has a nearly rectangular lattice, instead of the distinctly different square lattice for the more commonly observed well-ordered bilayer structure. This may be due to the dominance of intermolecular interactions within the monolayer when the influence from the substrate is shielded by the buffer layer. Density Functional Theory (DFT) calculations and Reduced Density Gradient (RDG) analysis indicate that the dominant intermolecular interaction within the unusual layer is likely the London dispersion force.
The Journal of Physical Chemistry
... Their data were fit satisfactorily with a = 1 and 2 5 n 5 4 . Although not directly comparabl... more ... Their data were fit satisfactorily with a = 1 and 2 5 n 5 4 . Although not directly comparable, the initial sticking coefficient at the same average normal kinetic energy reported by Hamza and Madix is very close to that obtained ... 1983, 135, (10) Gentle, TM; Muetterties, EL J. Phys. ...
Physical Review B
An adiabatic theory has been developed to describe spontaneous transfer of adatoms from a surface... more An adiabatic theory has been developed to describe spontaneous transfer of adatoms from a surface to a tip in atomic force microscopy and scanning tunneling microscopy ͑AFM/STM͒. It is shown that, at sufficiently low temperatures, the influence of phonon and electron-hole excitations on the transfer process may become so small that coherent transitions of an adatom between the surface and the tip are possible. The adatom tunnels back and forth between the surface and the tip with a definite period that depends on the surface-tip separation. The effect is mainly due to a unique opportunity to vary the tunneling amplitude of the adsorbate by controlling the tip-surface separation distance. Two features contribute to the quantum coherence phenomenon being even more pronounced as compared to that of interstitial hopping in the bulk: ͑a͒ the electron density of states at the Fermi level, and ͑b͒ the lattice deformations associated with the presence of the adsorbate outside the surface are noticeably smaller than for an interstitial in the bulk. As a result, electron and phonon polaron effects, respectively, which reduce the mobility of the adatom with respect to surface-tip transition, are substantially suppressed at all temperatures. For typical AFM/STM tip velocities and separation distances, the coherent transition rate of chemisorbed hydrogen atoms at temperatures below 10 K for insulators and semiconductors, and below 0.1 K for metals, may not only be comparable with but also exceed the thermally activated ͑incoherent͒ transfer rates at room temperature. ͓S0163-1829͑98͒08108-9͔
Physical Review B
Low-energy electron diffraction intensity vs voltage ͑LEED I-V͒ measurements and analysis are use... more Low-energy electron diffraction intensity vs voltage ͑LEED I-V͒ measurements and analysis are used to determine the multilayer surface relaxation of W͑110͒. Measurements and analysis are presented for both flat and vicinal surfaces, demonstrating that surface roughness leads to only small errors in LEED structure determinations. Flat, clean W͑110͒ exhibits first-(d 12) and second-(d 23) layer relaxations of Ϫ3.0Ϯ1.3% and ϩ0.2Ϯ1.3%, respectively, relative to the bulk lattice spacing d 0 ϭ2.237 Å. This experimentally determined surface relaxation of W͑110͒ is compatible with a recent combined density-functional theory calculation and LEED study ͓M.
Surface Science
The influence of a dissipative environment on quantum coherence in surface-tip adatom transfer in... more The influence of a dissipative environment on quantum coherence in surface-tip adatom transfer in AFM/STM is studied within an adiabatic approach, taking into account the slow motion of the tip with respect to an adsorption site, It is shown that coherent tunneling is the dominant mechanism of ada tom transfer at temperatures below 10 K for insulators and semiconductors, and below 0, I K for metals, The negative influence of electron and phonon polaron effects, which manifests itself in the destruction of coherence, may be noticeably compensated by potential fluctuations due to atom vibrations, As a result. the renormalized coherent tunneling amplitude may be even greater than the ground energy level splitting in the absence of a dissipative environment. Prospective pratical applications of the quantum coherence in adatom transfer are discussed,
Surface Science
In order to understand the unique properties of quasicrystalline surfaces, it is paramount to com... more In order to understand the unique properties of quasicrystalline surfaces, it is paramount to compare quasicrystalline and crystalline surfaces of similar chemical composition. To that end, the fivefold surface of an AlCuFe quasicrystal substrate was transformed, by ion bombardment and annealing, into a film with the b-Al(Cu 1−x Fe x) bulk structure. This is a CsCl structure with Fe and Cu atoms randomly occupying the body-center sites, and Al atoms at the corner sites. The film exposes a (110) free surface: its external structure was analyzed by dynamical low-energy electron diffraction in terms of atomic positions and layer-wise composition. The best fit between theory and experiment slightly favors a copper-rich composition in the surface layers (x=0), although the sensitivity to the value of x is low, because Cu and Fe are very similar electron scatterers. The Al atoms in the surface layer buckle outward by 0.12±0.04 Å relative to the Cu or Fe atoms in the same layer, while other relaxations from the bulk structure are small.
Physical chemistry chemical physics : PCCP, Jan 21, 2016
Rotation-inducing torque is ubiquitous in many molecular systems. We present a straightforward th... more Rotation-inducing torque is ubiquitous in many molecular systems. We present a straightforward theoretical method based on forces acting on atoms and obtained from atomistic quantum mechanics calculations to quickly and qualitatively determine whether a molecule or sub-unit thereof has a tendency to rotate and, if so, around which axis and in which sense: clockwise or counterclockwise. The method also indicates which atoms, if any, are predominant in causing the rotation. Our computational approach can in general efficiently provide insights into the internal rotational degrees of freedom of all molecules and help to theoretically screen or modify them in advance of experiments or to efficiently guide a detailed analysis of their rotational behavior with more extensive computations. As an example, we demonstrate the effectiveness of the approach using a specific light-driven molecular rotary motor which was successfully synthesized and analyzed in prior experiments and simulations.
Langmuir : the ACS journal of surfaces and colloids, Jan 5, 2017
We present a comparative study, combining density functional theory with scanning tunneling micro... more We present a comparative study, combining density functional theory with scanning tunneling microscopy/spectroscopy, of two aromatic molecules bonded with a variable number of Cu adatom(s) on a Cu(111) surface. The two molecules, 1,3,5-tris(pyridyl)benzene (TPyB) and 1,3,5-tris(4-radical-phenyl)benzene (TPB), possess the same aromatic backbone but bond weakly versus strongly to Cu with different terminal groups, respectively. We find that TPyB and TPB exhibit, respectively, small versus large charge transfers between the surface and the molecule; this contrast results in opposite shifts in the calculated density of states distributions and thus explains the opposite STS peak shifts observed in our experiments. The two molecules exhibit weak donor versus strong acceptor characters. This work provides a fundamental understanding, on a single-molecule level, of the principle that selecting specific functional groups can effectively and intentionally modify the molecular electronic prop...
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Papers by Michel Van Hove