Journal of chemical physics online/The Journal of chemical physics/Journal of chemical physics, Apr 16, 2024
Continuum or discrete polarizable models for the study of optoelectronic processes in embedded su... more Continuum or discrete polarizable models for the study of optoelectronic processes in embedded subsystems rely mostly on the restriction of the surrounding electronic dielectric response to its low frequency limit. Such a description hinges on the assumption that the electrons in the surrounding medium react instantaneously to any excitation in the central subsystem, treating thus the environment in the adiabatic limit. Exploiting a recently developed embedded GW formalism, with an environment described at the fully ab initio level, we assess the merits of the adiabatic limit with respect to an environment where the full dynamics of the dielectric response is considered. Further, we show how to properly take the static limit of the environment susceptibility, introducing the so-called Coulomb-hole and screened-exchange contributions to the reaction field. As a first application, we consider a C 60 molecule at the surface of a C 60 crystal, namely a case where the dynamics of the embedded and embedding subsystems are similar. The common adiabatic assumption, when properly treated, generates errors below 10% on the polarization energy associated with frontier energy levels and associated energy gaps. Finally, we consider a water molecule inside a metallic nanotube, the worst case for the environment adiabatic limit. The error on the gap polarization energy remains below 10%, even though the error on the frontier orbitals polarization energies can reach a few tenths of an electronvolt. 1
Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-a... more Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control.
We report on the synthesis of C 2n2q Si q clusters with 2n 32 2 100 and q , 4. The analysis of th... more We report on the synthesis of C 2n2q Si q clusters with 2n 32 2 100 and q , 4. The analysis of the abundance distribution and photofragmentation spectra provides clear evidences that such clusters remain in the fullerene geometry and that the Si atoms are located close to each other in the fullerene network. These results are corroborated by ab initio calculations within the density functional theory. The stability and electronic properties of these heterofullerenes are discussed.
The high pressure evolution of silicon clathrates is studied at room temperature by x-ray diffrac... more The high pressure evolution of silicon clathrates is studied at room temperature by x-ray diffraction up to 15 GPa. Remarkably, no transition towards the diamond structure is observed and the clathrate phase transforms directly into the b-tin metallic phase at 11 GPa. Further, the bulk modulus is found to be 90 6 5 GPa, that is, only ͑8 6 5͒% smaller than the one of the diamond phase. These results are in good agreement with ab initio calculations which predict further that carbon clathrates, if synthesized, should be less compressible than cubic BN.
We discuss the high pressure properties of different silicon clathrate structures that we have in... more We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.
As a result of the larger covalent radius of boron (r B = 0.88Å) when compared to that of carbon ... more As a result of the larger covalent radius of boron (r B = 0.88Å) when compared to that of carbon (r C = 0.77 Å), the introduction of substitutional boron into diamond leads to an expansion a/a of the lattice parameter. This has been found previously to follow a linear interpolation (Vegard law) as long as the boron content is lower than about 0.5 at.% in MPCVD epilayers or 1.5 at.% in HPHT bulk crystals. Above those concentrations, the expansion is less pronounced than predicted by Vegard. In order to explain this effect, we have performed ab initio calculations on C:B substitutional alloys. The results show that the presence of interstitial boron and of boron clusters is not necessary to explain the experimental data available in the literature. Moreover, quantitative estimates are proposed for the deformation potential of the valence band maximum and for the steric effect associated to boron pairing. We then apply these conclusions to discuss the different variations of a/a vs boron contents observed by high resolution XRD experiments performed on "insulating" and metallic (and superconducting) p ++ diamond epilayers grown by MPCVD on (100)-and (111)-oriented type Ib substrates, for which boron concentration profiles have been determined by Secondary Ion Mass Spectroscopy
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:
We present a first-principles calculation of the quasiparticule electronic structure of ethylene ... more We present a first-principles calculation of the quasiparticule electronic structure of ethylene adsorbed on the dimer reconstructed Si(001)-2×1 surface. Within the GW approximation, the self-energy corrections for the states derived from the molecular adsorbate are found to be much larger than those for the states derived from bulk silicon. The calculated quasiparticule band structure is in an excellent agreement with photoemission spectra, and cannot be obtained by a simple ``scissor operator'' correction to the local-density-approximation calculations. We also study the dependence of the GW correction on the localization of the wave functions. Finally, implications of the present results on the STM images of the adsorbed molecules are discussed.
... Phys. 108, 9868 (1998). [6] AJ Mayne et al., Surf. Sci. 284, 247 (1993). [7] H. Ness, AJ Fish... more ... Phys. 108, 9868 (1998). [6] AJ Mayne et al., Surf. Sci. 284, 247 (1993). [7] H. Ness, AJ Fisher, and GAD Briggs, Surf. Sci. 380, L479 (1997); H. Ness and AJ Fisher, J. Phys. Condens. ... [15] MS Hybertsen and SG Louie, Phys. Rev. Lett. 55, 1418 (1985); Phys. Rev. ...
Bulletin of the American Physical Society, Mar 15, 2017
photovoltaic (OPV) devices are a promising (cheap and versatile) technology for harvesting the so... more photovoltaic (OPV) devices are a promising (cheap and versatile) technology for harvesting the solar energy. Their efficiency depends critically on the charge transfer (CT) effects taking place at the interface between electron donor and acceptor phases. In order to theoretically devise new OPV devices with high efficiency, it is thus important to describe these CT effects adequately. Tens of thousands of donor molecules have been already tested in a multiple-step screening within the Harvard Clean Energy Project (CEP), leading to a ranking of potential candidates. However, these calculations have been performed relying on density-functional theory. The latter is known to underestimate the band gap and not to describe electron-hole interaction and CT effects correctly. Here, we investigate the top 20 donor molecules from the CEP ranking using the GW /BSE formalism.
We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical tech... more We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical techniques. Electron microscopy observations and electron diffraction patterns reveal that B doping considerably increases the length of carbon tubes and leads to a remarkable preferred zigzag chirality. These findings are corroborated by first-principles static and dynamical simulations which indicate that, in the zigzag geometry, B atoms act as a surfactant during growth, preventing tube closure. This mechanism does not extend to armchair tubes, suggesting a helicity selection during growth.
Changes in the electronic structure of multiwalled nanotubes due to the introduction of boron in ... more Changes in the electronic structure of multiwalled nanotubes due to the introduction of boron in the lattice are identified using scanning tunneling spectroscopy. Doped tubes are metallic with no apparent band gap, in contrast to undoped tubes with varying electronic character. Combined with ab initio calculations, we show that changes in the local density of states, as determined from tunneling spectroscopy, must be interpreted in terms of nanodomains of dopant islands and not as isolated substitutional species. [S0031-9007(98)07103-8]
Ab initio photoabsorption cross sections of small silicon and alkali clusters (Li, Na) have been ... more Ab initio photoabsorption cross sections of small silicon and alkali clusters (Li, Na) have been calculated by a new method. Different structural isomers of a given silicon cluster give rise to clearly distinguishable spectra. Inclusion of screening effects is shown to be essential to describe the spectra. We propose that comparison of theoretical spectra with measured ones would serve as a useful tool to discern the structure of small semiconductor clusters. Low temperature measurements and/or line-shape analysis are needed to extract detailed structural information from the spectra of alkali clusters because of the collective character of the main resonance. [S0031-9007(96)00571-6]
Bethe–Salpeter equation (BSE) many-body Greens function formalism provides excess dipole moments ... more Bethe–Salpeter equation (BSE) many-body Greens function formalism provides excess dipole moments (Δμ) on the same level or slightly better than that of TD-DFT relying on M06-2X and RSH functionals.
Charge carriers energetics is key in electron transfer processes such as those that enable the el... more Charge carriers energetics is key in electron transfer processes such as those that enable the electrical doping of organic semiconductors. In this study, we take advantage of the quantitative accuracy of embedded GW calculations to perform a series of virtual experiments that allow measuring the electron affinity of p-type dopants in different host solids. Our calculations show that the energy levels of a molecular impurity strongly depend on the host environment as a result of electrostatic intermolecular interactions. In particular, the electron affinity of a dopant impurity in a given semiconductor is found to be up to 1 eV lower than that of the pure dopant crystal. This result questions the pertinence of the electron affinity measured for pure dopants in order to predict doping efficiency in a specific host. The role of the Coulomb electron-hole interaction for the dopant-tosemiconductor charge transfer and for the release of doping-induced charges is discussed.
We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbac... more We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbacteriochlorin dyad, a paradigmatic photosynthetic complex. In great contrast with standard timedependent density functional theory calculations with (semi)local kernels, charge transfer excitations are correctly located above the intramolecular Q-bands transitions found to be in excellent agreement with experiment. Further, the asymptotic Coulomb behavior towards the true quasiparticle gap for charge transfer excitations at long distance is correctly reproduced, showing that the present scheme allows to study with the same accuracy intramolecular and charge transfer excitations at various spatial range and screening environment without any adjustable parameter.
Using a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), ... more Using a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), CASPT2, time-dependent density functional theory (TD-DFT), and BSE/evGW, the two latter combined with different exchange-correlation functionals, we investigate the lowest singlet transition in 23 n→π* compounds based on the nitroso, thiocarbonyl, carbonyl, and diazo chromophores. First, for 16 small derivatives we compare the transition energies provided by the different wave function approaches to define theoretical best estimates. For this set, it surprisingly turned out that ADC(2) offers a better match with CC3 than ADC(3). Next, we use 10 functionals belonging to the "LYP" and "M06" families and compare the TD-DFT and the BSE/evGW descriptions. The BSE/evGW results are less sensitive than their TD-DFT counterparts to the selected functional, especially in the M06 series. Nevertheless, BSE/evGW delivers larger errors than TD-CAM-B3LYP, which provides extremely accurate results in the present case, especially when the Tamm-Dancoff approximation is applied. In addition, we show that, among the different starting points for BSE/evGW calculations, M06-2X eigenstates stand as the most appropriate. Finally, we confirm that the trends observed on the small compounds pertain in larger molecules.
The analytic continuation of the GW self-energy from the imaginary to the real energy axis is a c... more The analytic continuation of the GW self-energy from the imaginary to the real energy axis is a central difficulty for approaches exploiting the favourable properties of response functions at imaginary frequencies. Within a scheme merging contourdeformation and analytic-continuation techniques, we show on the basis of extensive calculations for large molecular sets that it is preferable to perform an analytic continuation of the dynamically screened Coulomb potential W rather than the much more structured self-energy operator. The case of states lying far away from the gap, including core states, is addressed by generalizing the analytic continuation scheme, accounting further for quasiparticle lifetimes.
Journal of chemical physics online/The Journal of chemical physics/Journal of chemical physics, Apr 16, 2024
Continuum or discrete polarizable models for the study of optoelectronic processes in embedded su... more Continuum or discrete polarizable models for the study of optoelectronic processes in embedded subsystems rely mostly on the restriction of the surrounding electronic dielectric response to its low frequency limit. Such a description hinges on the assumption that the electrons in the surrounding medium react instantaneously to any excitation in the central subsystem, treating thus the environment in the adiabatic limit. Exploiting a recently developed embedded GW formalism, with an environment described at the fully ab initio level, we assess the merits of the adiabatic limit with respect to an environment where the full dynamics of the dielectric response is considered. Further, we show how to properly take the static limit of the environment susceptibility, introducing the so-called Coulomb-hole and screened-exchange contributions to the reaction field. As a first application, we consider a C 60 molecule at the surface of a C 60 crystal, namely a case where the dynamics of the embedded and embedding subsystems are similar. The common adiabatic assumption, when properly treated, generates errors below 10% on the polarization energy associated with frontier energy levels and associated energy gaps. Finally, we consider a water molecule inside a metallic nanotube, the worst case for the environment adiabatic limit. The error on the gap polarization energy remains below 10%, even though the error on the frontier orbitals polarization energies can reach a few tenths of an electronvolt. 1
Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-a... more Organic solar cells usually utilise a heterojunction between electron-donating (D) and electron-accepting (A) materials to split excitons into charges. However, the use of D-A blends intrinsically limits the photovoltage and introduces morphological instability. Here, we demonstrate that polycrystalline films of chemically identical molecules offer a promising alternative and show that photoexcitation of α-sexithiophene (α-6T) films results in efficient charge generation. This leads to α-6T based homojunction organic solar cells with an external quantum efficiency reaching up to 44% and an open-circuit voltage of 1.61 V. Morphological, photoemission, and modelling studies show that boundaries between α-6T crystalline domains with different orientations generate an electrostatic landscape with an interfacial energy offset of 0.4 eV, which promotes the formation of hybridised exciton/charge-transfer states at the interface, dissociating efficiently into free charges. Our findings open new avenues for organic solar cell design where material energetics are tuned through molecular electrostatic engineering and mesoscale structural control.
We report on the synthesis of C 2n2q Si q clusters with 2n 32 2 100 and q , 4. The analysis of th... more We report on the synthesis of C 2n2q Si q clusters with 2n 32 2 100 and q , 4. The analysis of the abundance distribution and photofragmentation spectra provides clear evidences that such clusters remain in the fullerene geometry and that the Si atoms are located close to each other in the fullerene network. These results are corroborated by ab initio calculations within the density functional theory. The stability and electronic properties of these heterofullerenes are discussed.
The high pressure evolution of silicon clathrates is studied at room temperature by x-ray diffrac... more The high pressure evolution of silicon clathrates is studied at room temperature by x-ray diffraction up to 15 GPa. Remarkably, no transition towards the diamond structure is observed and the clathrate phase transforms directly into the b-tin metallic phase at 11 GPa. Further, the bulk modulus is found to be 90 6 5 GPa, that is, only ͑8 6 5͒% smaller than the one of the diamond phase. These results are in good agreement with ab initio calculations which predict further that carbon clathrates, if synthesized, should be less compressible than cubic BN.
We discuss the high pressure properties of different silicon clathrate structures that we have in... more We discuss the high pressure properties of different silicon clathrate structures that we have investigated by means of X-ray diffraction and ab initio calculations. Compressibility, transition pressures or phase transformations are interpreted as a function of the nature of the guest atom intercalation. The compressibility of the clathrate structure is in all cases close to that of silicon diamond whereas transition pressures or the high pressure phases are extremely depending on the nature of the guest atom. We address the implications for obtaining a metallic material as hard as diamond.
As a result of the larger covalent radius of boron (r B = 0.88Å) when compared to that of carbon ... more As a result of the larger covalent radius of boron (r B = 0.88Å) when compared to that of carbon (r C = 0.77 Å), the introduction of substitutional boron into diamond leads to an expansion a/a of the lattice parameter. This has been found previously to follow a linear interpolation (Vegard law) as long as the boron content is lower than about 0.5 at.% in MPCVD epilayers or 1.5 at.% in HPHT bulk crystals. Above those concentrations, the expansion is less pronounced than predicted by Vegard. In order to explain this effect, we have performed ab initio calculations on C:B substitutional alloys. The results show that the presence of interstitial boron and of boron clusters is not necessary to explain the experimental data available in the literature. Moreover, quantitative estimates are proposed for the deformation potential of the valence band maximum and for the steric effect associated to boron pairing. We then apply these conclusions to discuss the different variations of a/a vs boron contents observed by high resolution XRD experiments performed on "insulating" and metallic (and superconducting) p ++ diamond epilayers grown by MPCVD on (100)-and (111)-oriented type Ib substrates, for which boron concentration profiles have been determined by Secondary Ion Mass Spectroscopy
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:
We present a first-principles calculation of the quasiparticule electronic structure of ethylene ... more We present a first-principles calculation of the quasiparticule electronic structure of ethylene adsorbed on the dimer reconstructed Si(001)-2×1 surface. Within the GW approximation, the self-energy corrections for the states derived from the molecular adsorbate are found to be much larger than those for the states derived from bulk silicon. The calculated quasiparticule band structure is in an excellent agreement with photoemission spectra, and cannot be obtained by a simple ``scissor operator'' correction to the local-density-approximation calculations. We also study the dependence of the GW correction on the localization of the wave functions. Finally, implications of the present results on the STM images of the adsorbed molecules are discussed.
... Phys. 108, 9868 (1998). [6] AJ Mayne et al., Surf. Sci. 284, 247 (1993). [7] H. Ness, AJ Fish... more ... Phys. 108, 9868 (1998). [6] AJ Mayne et al., Surf. Sci. 284, 247 (1993). [7] H. Ness, AJ Fisher, and GAD Briggs, Surf. Sci. 380, L479 (1997); H. Ness and AJ Fisher, J. Phys. Condens. ... [15] MS Hybertsen and SG Louie, Phys. Rev. Lett. 55, 1418 (1985); Phys. Rev. ...
Bulletin of the American Physical Society, Mar 15, 2017
photovoltaic (OPV) devices are a promising (cheap and versatile) technology for harvesting the so... more photovoltaic (OPV) devices are a promising (cheap and versatile) technology for harvesting the solar energy. Their efficiency depends critically on the charge transfer (CT) effects taking place at the interface between electron donor and acceptor phases. In order to theoretically devise new OPV devices with high efficiency, it is thus important to describe these CT effects adequately. Tens of thousands of donor molecules have been already tested in a multiple-step screening within the Harvard Clean Energy Project (CEP), leading to a ranking of potential candidates. However, these calculations have been performed relying on density-functional theory. The latter is known to underestimate the band gap and not to describe electron-hole interaction and CT effects correctly. Here, we investigate the top 20 donor molecules from the CEP ranking using the GW /BSE formalism.
We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical tech... more We investigate the growth of B-doped carbon nanotubes combining experimental and theoretical techniques. Electron microscopy observations and electron diffraction patterns reveal that B doping considerably increases the length of carbon tubes and leads to a remarkable preferred zigzag chirality. These findings are corroborated by first-principles static and dynamical simulations which indicate that, in the zigzag geometry, B atoms act as a surfactant during growth, preventing tube closure. This mechanism does not extend to armchair tubes, suggesting a helicity selection during growth.
Changes in the electronic structure of multiwalled nanotubes due to the introduction of boron in ... more Changes in the electronic structure of multiwalled nanotubes due to the introduction of boron in the lattice are identified using scanning tunneling spectroscopy. Doped tubes are metallic with no apparent band gap, in contrast to undoped tubes with varying electronic character. Combined with ab initio calculations, we show that changes in the local density of states, as determined from tunneling spectroscopy, must be interpreted in terms of nanodomains of dopant islands and not as isolated substitutional species. [S0031-9007(98)07103-8]
Ab initio photoabsorption cross sections of small silicon and alkali clusters (Li, Na) have been ... more Ab initio photoabsorption cross sections of small silicon and alkali clusters (Li, Na) have been calculated by a new method. Different structural isomers of a given silicon cluster give rise to clearly distinguishable spectra. Inclusion of screening effects is shown to be essential to describe the spectra. We propose that comparison of theoretical spectra with measured ones would serve as a useful tool to discern the structure of small semiconductor clusters. Low temperature measurements and/or line-shape analysis are needed to extract detailed structural information from the spectra of alkali clusters because of the collective character of the main resonance. [S0031-9007(96)00571-6]
Bethe–Salpeter equation (BSE) many-body Greens function formalism provides excess dipole moments ... more Bethe–Salpeter equation (BSE) many-body Greens function formalism provides excess dipole moments (Δμ) on the same level or slightly better than that of TD-DFT relying on M06-2X and RSH functionals.
Charge carriers energetics is key in electron transfer processes such as those that enable the el... more Charge carriers energetics is key in electron transfer processes such as those that enable the electrical doping of organic semiconductors. In this study, we take advantage of the quantitative accuracy of embedded GW calculations to perform a series of virtual experiments that allow measuring the electron affinity of p-type dopants in different host solids. Our calculations show that the energy levels of a molecular impurity strongly depend on the host environment as a result of electrostatic intermolecular interactions. In particular, the electron affinity of a dopant impurity in a given semiconductor is found to be up to 1 eV lower than that of the pure dopant crystal. This result questions the pertinence of the electron affinity measured for pure dopants in order to predict doping efficiency in a specific host. The role of the Coulomb electron-hole interaction for the dopant-tosemiconductor charge transfer and for the release of doping-induced charges is discussed.
We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbac... more We study using the Bethe-Salpeter formalism the excitation energies of the zincbacteriochlorinbacteriochlorin dyad, a paradigmatic photosynthetic complex. In great contrast with standard timedependent density functional theory calculations with (semi)local kernels, charge transfer excitations are correctly located above the intramolecular Q-bands transitions found to be in excellent agreement with experiment. Further, the asymptotic Coulomb behavior towards the true quasiparticle gap for charge transfer excitations at long distance is correctly reproduced, showing that the present scheme allows to study with the same accuracy intramolecular and charge transfer excitations at various spatial range and screening environment without any adjustable parameter.
Using a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), ... more Using a large panel of theoretical approaches, namely, CC2, CCSD, CCSDR(3), CC3, ADC(2), ADC(3), CASPT2, time-dependent density functional theory (TD-DFT), and BSE/evGW, the two latter combined with different exchange-correlation functionals, we investigate the lowest singlet transition in 23 n→π* compounds based on the nitroso, thiocarbonyl, carbonyl, and diazo chromophores. First, for 16 small derivatives we compare the transition energies provided by the different wave function approaches to define theoretical best estimates. For this set, it surprisingly turned out that ADC(2) offers a better match with CC3 than ADC(3). Next, we use 10 functionals belonging to the "LYP" and "M06" families and compare the TD-DFT and the BSE/evGW descriptions. The BSE/evGW results are less sensitive than their TD-DFT counterparts to the selected functional, especially in the M06 series. Nevertheless, BSE/evGW delivers larger errors than TD-CAM-B3LYP, which provides extremely accurate results in the present case, especially when the Tamm-Dancoff approximation is applied. In addition, we show that, among the different starting points for BSE/evGW calculations, M06-2X eigenstates stand as the most appropriate. Finally, we confirm that the trends observed on the small compounds pertain in larger molecules.
The analytic continuation of the GW self-energy from the imaginary to the real energy axis is a c... more The analytic continuation of the GW self-energy from the imaginary to the real energy axis is a central difficulty for approaches exploiting the favourable properties of response functions at imaginary frequencies. Within a scheme merging contourdeformation and analytic-continuation techniques, we show on the basis of extensive calculations for large molecular sets that it is preferable to perform an analytic continuation of the dynamically screened Coulomb potential W rather than the much more structured self-energy operator. The case of states lying far away from the gap, including core states, is addressed by generalizing the analytic continuation scheme, accounting further for quasiparticle lifetimes.
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