研究目的
To investigate the effect of electronic excitation on the out-of-plane van der Waals bonds in layered materials, specifically MoS2 bilayers, using non-adiabatic quantum molecular dynamics simulations.
研究成果
The study demonstrates a strong and rapid athermal contraction of the out-of-plane lattice parameter in MoS2 bilayers upon electronic excitation, due to redistribution of electron density that increases both attractive and repulsive interactions between layers, with incomplete cancellation leading to net attraction. This behavior has potential applications for modulating properties in materials with non-covalent interactions.
研究不足
Simulations were performed at high charge carrier densities (around 10^21 cm^-3) in the electron-hole plasma regime, which is three orders of magnitude higher than experimental densities (10^18 cm^-3) in the excitonic regime. This leads to differences in magnitude and timescale of observed effects compared to experiments. The DFT-D method for van der Waals forces is insensitive to electronic charge density redistribution, which may not capture all effects.
1：Experimental Design and Method Selection:
Non-adiabatic quantum molecular dynamics (NAQMD) simulations were used to model atomic motion in photoexcited MoS2 bilayers. Adiabatic electronic structure was calculated using density functional theory (DFT) with the projector-augmented-wave method and generalized gradient approximation (GGA). Van der Waals interactions were estimated using the DFT-D approximation. NAQMD followed trajectories of atoms with electronic excitations and nonadiabatic transitions based on time-dependent density functional theory (TDDFT) and surface-hopping approaches.
2：Sample Selection and Data Sources:
The simulation cell consisted of a MoS2 bilayer in the 2H structure with 72 Mo atoms and 144 S atoms, spanning 19.14 × 19.14 × 22.34 ?. The system was modeled at 10 K.
3：14 × 14 × 34 ?. The system was modeled at 10 K.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Computational simulations were performed; no physical equipment was used. Software implementations for QMD and NAQMD simulations were employed.
4：Experimental Procedures and Operational Workflow:
Electronic excitation was modeled by modifying occupancy of Kohn-Sham energy levels at t=0, propagated using TDDFT. Surface hopping was used for non-adiabatic electron dynamics. Inter-layer distance was monitored over time for various excited charge carrier densities. Adiabatic molecular dynamics (AMD) simulations were performed for comparison.
5：Data Analysis Methods:
Forces on atoms were decomposed into attractive and repulsive components. Bond overlap populations (BOP) were calculated using Mulliken analysis. Charge redistribution was analyzed through planar-averaged electronic charge density.
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