Excited-State Forces with the Gaussian and Augmented Plane Wave Method for the Tamm-Dancoff Approximation of...

Area of Science:

• Computational Chemistry
• Quantum Mechanics
• Materials Science

Background:

• Augmented plane wave (APW) methods offer efficient electronic density descriptions for localized features.
• Existing APW implementations focus on ground-state properties and excitation energies.
• Accurate calculation of excited-state nuclear gradients is computationally demanding.

Purpose of the Study:

• Extend the Gaussian and augmented plane wave (GAPW) method to compute excited-state nuclear gradients.
• Implement this extension within the Tamm-Dancoff approximation (TDA) of time-dependent density functional theory (TD-DFT).
• Validate the method's accuracy and assess its applicability for extended systems.

Main Methods:

• Extension of the Gaussian and augmented plane wave (GAPW) method.
• Application of the Tamm-Dancoff approximation (TDA) within time-dependent density functional theory (TD-DFT).
• Implementation in the CP2K program package.

Main Results:

• Achieved maximum errors in nuclear forces for excited states below 0.1 eV/Å for 35 small molecules.
• Accurately reproduced the zero-phonon line of defective hexagonal boron nitride.
• Obtained errors of 0.6 eV (vs. GW-BSE) and 0.4 eV (vs. experiment) for the zero-phonon line.

Conclusions:

• The developed method provides accurate excited-state nuclear gradients.
• The approach is validated for molecular systems and extended materials.
• This advancement enables large-scale computations of excited-state properties in extended systems.