The GW-Method in Quantum Chemistry context: Theory, Implementation, and Benchmarks

In this contribution we describe our G0W0 implementation in the quantum chemistry package TURBOMOLE. In contrast to many other implementations we use a spectral representation of the response function enabling the analytic evaluation of energy integrals and derivatives. The four center integrals occurring in the expressions for the matrix elements of the self-energy are evaluated using the Resolution of the Identity (RI) method. The implementation is tested using a typical set of molecules (including e.g.: H2 – Cs2, methane – propane, benzene – naphacene, SF4, SiH4, Au4. We confirm that using G0W0 the deviation with experimental ionization energies is decreased by an order of magnitude, with respect to the single particle energy levels of DFT using GGA or hybrid functionals [PRB 81, 085103 (2010)]. Moreover, we see that the dependence of the G0W0 results on the functional of the underlying DFT calculation is minor. Current activities are focused on partial self-consistency, i.e. GW0. Future plans include the implementations needed for open shell, spin polarized, systems, symmetry and optical excitation spectra using the Bethe Salpeter equation

Avoiding asymptotic divergence of the potential from orbital- and energy-dependent exchange-correlation functionals

We investigate the asymptotic behavior of the exchange-correlation potentials deriving from orbital- and energy-dependent (OED) functionals potentially able to describe van der Waals interactions. We take some simple functionals based on the adiabatic connection fluctuation-dissipation (ACFD) theorem as examples. Although the potentials deriving from arbitrary OED functionals can be expected to diverge asymptotically, we find that these ACFD potentials are in fact well behaved. They indeed depend on Kohn-Sham orbitals and energies only through the Kohn-Sham Green function, allowing for complete analytical treatment. However, the dependence on the empty Kohn-Sham orbitals and energies must be treated with care. We discuss some precautions to be taken for practical calculation of these potentials. Last, we introduce approximate potentials, which are much simpler to compute than the exact ones, but are still quite accurate. (C) 2004 Wiley Periodicals, Inc