研究目的
To develop and validate an LCAO framework for velocity-gauge real-time TDDFT simulations in solids using range-separated hybrid functionals, enabling the study of valence and core excitonic effects in materials like Si, LiF, and h-BN.
研究成果
The LCAO framework for GKS VG-RT-TDDFT is validated against planewave methods and experiment, showing good agreement for valence and core excitations in solids. It enables efficient simulations of excitonic effects and light-matter interactions, with potential applications in spectroscopy. Future work should explore modified range-separation schemes for improved core-level accuracy.
研究不足
The LCAO basis sets have less variational freedom compared to planewaves, leading to discrepancies at higher conduction band energies. For core excitations, the range-separated hybrid functionals may not adequately capture short-range exchange effects, requiring global hybrids for better accuracy. Computational cost is high due to the evaluation of nonlocal exchange integrals.
1：Experimental Design and Method Selection:
The study employs a linear combination of atomic orbitals (LCAO) approach for velocity-gauge real-time TDDFT (VG-RT-TDDFT) with range-separated hybrid functionals. It extends a previous ALDA framework to include nonlocal exchange, using the time-dependent Generalized Kohn-Sham (TDGKS) equations in the velocity gauge.
2：Sample Selection and Data Sources:
Prototypical solid-state materials are used: bulk Si, bulk LiF, and monolayer hexagonal-BN (h-BN). Data for comparison comes from planewave simulations (e.g., using VASP) and experimental references.
3：List of Experimental Equipment and Materials:
Computational simulations are performed using an in-house development version of the SIESTA code for LCAO and VASP for planewave PAW simulations. Basis sets include numerical atomic orbitals (NAOs) and Gaussian-type orbitals (GTOs) for integral evaluation. Pseudopotentials are norm-conserving LDA types.
4：Experimental Procedures and Operational Workflow:
Groundstate band structures are computed using DFT with LDA and hybrid functionals. For TDDFT, a delta-function electric field pulse is applied, and the time-dependent current is propagated using a Crank-Nicholson scheme with predictor-corrector. Frequency-domain responses are obtained via Fourier transform. Core excitations are simulated by including 1s core states explicitly.
5：Data Analysis Methods:
Band gaps and dielectric functions are compared with planewave results and experiment. Excitonic effects are analyzed by examining peak positions and intensities in the optical spectra.
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