Imaginary-time time-dependent density functional theory for periodic systems.

Area of Science:

• Computational Physics
• Quantum Chemistry
• Materials Science

Background:

• Traditional self-consistent-field (SCF) methods in density functional theory (DFT) can face convergence challenges.
• Imaginary-time time-dependent density functional theory (it-TDDFT) has emerged as a potential alternative for ground-state calculations.
• Previous it-TDDFT applications focused on atomic clusters, showing promise where SCF methods faltered.

Purpose of the Study:

• To implement and validate imaginary-time time-dependent density functional theory (it-TDDFT) propagation for periodic systems.
• To assess the performance of it-TDDFT in comparison to SCF methods for challenging electronic structure calculations.
• To explore methods for accelerating it-TDDFT convergence in periodic systems.

Main Methods:

• Modified the Quantum ESPRESSO (QE) package to incorporate it-TDDFT propagation for periodic systems.
• Utilized a plane-wave basis set with multiple k-points, supporting non-collinear and DFT + U calculations.
• Tested it-TDDFT with ultra-soft and norm-conserving pseudopotentials.

Main Results:

• Successfully implemented and verified it-TDDFT propagation for periodic systems, including DFT + U non-collinear and ultra-soft pseudopotential calculations.
• Demonstrated that it-TDDFT converges to the exact SCF energy in most cases, providing a reliable alternative for difficult systems.
• Showed that adaptive-size imaginary time-steps can significantly accelerate convergence for different kinetic energy plane-waves.

Conclusions:

• The implemented it-TDDFT method provides a viable and often more reliable alternative to SCF for obtaining ground-state properties in periodic systems.
• it-TDDFT shows particular utility in cases where standard SCF convergence is problematic.
• Adaptive time-stepping strategies offer a pathway to enhance the efficiency of it-TDDFT calculations for periodic materials.