Charge transfer excitations with range separated functionals using improved virtual orbitals

TL;DR

This paper introduces an implementation of range separated functionals with improved virtual orbitals in the projector augmented waves method, enhancing the accuracy and convergence of charge transfer excitation calculations.

Contribution

The authors develop a new implementation using the Slater-function on grids and Huzinaga's virtual orbitals to improve convergence and accuracy in charge transfer excitation computations.

Findings

Convergence is slow with standard linear response TDDFT and canonical Fock orbitals.

Using Huzinaga's virtual orbitals significantly improves convergence.

Ground-state calculations with this method accurately describe long-range charge transfer excitations.

Abstract

We present an implementation of range separated functionals utilizing the Slater-function on grids in real space in the projector augmented waves method. The screened Poisson equation is solved to evaluate the necessary screened exchange integrals on Cartesian grids. The implementation is verified against existing literature and applied to the description of charge transfer excitations. We find very slow convergence for calculations within linear response time-dependent density functional theory and unoccupied orbitals of the canonical Fock operator. Convergence can be severely improved by using Huzinaga's virtual orbitals instead. This combination furthermore enables an accurate determination of long-range charge transfer excitations by means of ground-state calculations.