The GW-technology corrects the Kohn–Sham (KS) single particle energies and single particle states for artifacts of the exchange-correlation (XC) functional of the underlying density functional theory ...(DFT) calculation. We present the formalism and implementation of GW adapted for standard quantum chemistry packages. Our implementation is tested using a typical set of molecules. We find that already after the first iteration of the self-consistency cycle, G 0 W 0, the deviations of quasi-particle energies from experimental ionization potentials and electron affinities can be reduced by an order of magnitude against those of KS-DFT using GGA or hybrid functionals. Also, we confirm that even on this level of approximation there is a considerably diminished dependency of the G 0 W 0-results on the XC-functional of the underlying DFT.
We present the formalism and implementation of quasi-particle self-consistent GW (qsGW) and eigenvalue only quasi-particle self-consistent GW (evGW) adapted to standard quantum chemistry packages. ...Our implementation is benchmarked against high-level quantum chemistry computations (coupled-cluster theory) and experimental results using a representative set of molecules. Furthermore, we compare the qsGW approach for five molecules relevant for organic photovoltaics to self-consistent GW results (scGW) and analyze the effects of the self-consistency on the ground state density by comparing calculated dipole moments to their experimental values. We show that qsGW makes a significant improvement over conventional G 0 W 0 and that partially self-consistent flavors (in particular evGW) can be excellent alternatives.
A series of auxiliary basis sets to fit Coulomb potentials for the elements H to Rn (except lanthanides) is presented. For each element only one auxiliary basis set is needed to approximate Coulomb ...energies in conjunction with orbital basis sets of split valence, triple zeta valence and quadruple zeta valence quality with errors of typically below ca. 0.15 kJ mol(-1) per atom; this was demonstrated in conjunction with the recently developed orbital basis sets of types def2-SV(P), def2-TZVP and def2-QZVPP for a large set of small molecules representing (nearly) each element in all of its common oxidation states. These auxiliary bases are slightly more than three times larger than orbital bases of split valence quality. Compared to non-approximated treatments, computation times for the Coulomb part are reduced by a factor of ca. 8 for def2-SV(P) orbital bases, ca. 25 for def2-TZVP and ca. 100 for def2-QZVPP orbital bases.
The GW method in its most widespread variant takes, as an input, Kohn–Sham (KS) single particle energies and single particle states and yields results for the single-particle excitation energies that ...are significantly improved over the bare KS estimates. Fundamental shortcomings of density functional theory (DFT) when applied to excitation energies as well as artifacts introduced by approximate exchange-correlation (XC) functionals are thus reduced. At its heart lies the quasi-particle (qp) equation, whose solution yields the corrected excitation energies and qp-wave functions. We propose an efficient approximation scheme to treat this equation based on second-order perturbation theory and self-consistent iteration schemes. We thus avoid solving (large) eigenvalue problems at the expense of a residual error that is comparable to the intrinsic uncertainty of the GW truncation scheme and is, in this sense, insignificant.
Gaussian basis sets of quadruple zeta valence quality for Rb-Rn are presented, as well as bases of split valence and triple zeta valence quality for H-Rn. The latter were obtained by (partly) ...modifying bases developed previously. A large set of more than 300 molecules representing (nearly) all elements-except lanthanides-in their common oxidation states was used to assess the quality of the bases all across the periodic table. Quantities investigated were atomization energies, dipole moments and structure parameters for Hartree-Fock, density functional theory and correlated methods, for which we had chosen Møller-Plesset perturbation theory as an example. Finally recommendations are given which type of basis set is used best for a certain level of theory and a desired quality of results.
We investigate electronic transport through single conjugated molecules, and compare our data to results of quantum chemical calculations. Conductance spectra of two types of molecules are studied in ...a metal–molecule–metal junction established using the mechanically controlled break-junction technique. We observe a suppressed conductance at low bias, characteristic step-like features at higher voltages, and strong sample-to-sample fluctuations. We develop a quantum-chemical model for our system using DFT calculations, with the electrodes modelled by small clusters. We consider the effects of different geometries of molecule–metal configurations and bonding as well as finite electric field, and are thereby able to account for the phenomenology of the experimental data.
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