koopmans: An Open-Source Package for Accurately and Efficiently Predicting Spectral Properties with Koopmans...

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Materials Science

Background:

• Semilocal Density Functional Theory (DFT) often exhibits a mismatch between Kohn-Sham orbital energies and electron removal/addition energies.
• This mismatch is a primary cause of the band gap problem and inaccuracies in predicting spectral properties.
• Existing methods for accurate spectral property prediction can be computationally expensive.

Purpose of the Study:

• To present the theory and implementation of Koopmans functionals.
• To introduce an open-source package for performing Koopmans functional calculations.
• To provide a computationally efficient and accurate method for predicting spectral properties.

Main Methods:

• Development of Koopmans functionals based on an orbital-density-dependent functional framework.
• Imposition of a generalized piecewise linearity condition on the electronic manifold.
• Implementation of necessary algorithms for practical calculations.

Main Results:

• Koopmans functionals ensure orbital energies match electron removal/addition energy differences.
• Achieved accuracy comparable to many-body perturbation theory for molecular orbital energies and solid-state band structures.
• Significantly reduced computational cost compared to traditional methods.

Conclusions:

• Koopmans functionals provide a powerful and computationally efficient approach for accurate spectral property prediction.
• The developed open-source package 'koopmans' facilitates reliable calculations for molecules and materials.
• This method addresses fundamental limitations of semilocal DFT in spectral property calculations.