Nonlinear electronic excitations in crystalline solids using meta-generalized gradient approximation and hybrid...

Area of Science:

• Computational Physics
• Materials Science
• Quantum Chemistry

Background:

• Accurate calculation of electron dynamics in crystalline solids is crucial for understanding material properties.
• Real-time time-dependent density functional theory (TDDFT) is a powerful tool, but its accuracy depends on the choice of exchange-correlation potentials.
• Existing potentials may not accurately reproduce band gap energies, impacting the simulation of electronic excitations.

Purpose of the Study:

• To develop and refine methods for real-time TDDFT calculations of electron dynamics in crystalline solids.
• To evaluate the performance of different exchange-correlation potentials (TB-mBJ, HSE, LDA) in simulating electronic excitations.
• To investigate the influence of laser intensity on electronic excitation energies.

Main Methods:

• Implementation of predictor-corrector steps for stable time evolution with the TB-mBJ potential.
• Development of a method to calculate electronic excitation energy independent of the energy functional for TB-mBJ.
• Adaptation of the HSE functional for efficient computation on massively parallel GPU systems using Fourier space.
• Comparison of electronic excitations in silicon and germanium induced by femtosecond laser pulses using TB-mBJ, HSE, and LDA.

Main Results:

• The predictor-corrector step was found necessary for stable time evolution with the TB-mBJ potential.
• A novel method for evaluating electronic excitation energy was developed for the TB-mBJ potential.
• An efficient method for the HSE functional was developed for massive parallel computation.
• At low laser intensities, electronic excitations are sensitive to band gap energies, showing similar results for TB-mBJ and HSE, and smaller values for LDA.
• At high laser intensities, the differences in electronic excitation energies among the three potentials diminish.

Conclusions:

• The developed methods enhance the accuracy and efficiency of real-time TDDFT calculations.
• The choice of exchange-correlation potential significantly impacts the simulation of electronic excitations at low laser intensities.
• At high laser intensities, the electronic excitation energies become less dependent on the specific potential used.