Ab initio electron-lattice downfolding: potential energy landscapes, anharmonicity, and molecular dynamics in charge density wave materials

Abstract

The interplay of electronic and nuclear degrees of freedom presents an outstanding problem in condensed matter physics and chemistry. Computational challenges arise especially for large systems, long time scales, in nonequilibrium, or in systems with strong correlations. In this work, we show how downfolding approaches facilitate complexity reduction on the electronic side and thereby boost the simulation of electronic properties and nuclear motion - in particular molecular dynamics (MD) simulations. Three different downfolding strategies based on constraining, unscreening, and combinations thereof are benchmarked against full density functional calculations for selected charge density wave (CDW) systems, namely 1H-TaS${}_2$, 1T-TiSe${}_2$, 1H-NbS${}_2$, and a one-dimensional carbon chain. We find that the downfolded models can reproduce potential energy surfaces on supercells accurately and facilitate computational speedup in MD simulations by about five orders of magnitude in comparison to purely ab initio calculations. For monolayer 1H-TaS${}_2$ we report classical replica exchange and quantum path integral MD simulations, revealing the impact of thermal and quantum fluctuations on the CDW transition.

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Cited by in corpus (8)

• i-PI 3.0: a flexible and efficient framework for advanced atomistic simulations
• Unconventional charge-density-wave gap in monolayer NbS${}_2$
• Exciton-exciton interactions in van der Waals heterobilayers
• Compressing Hamiltonians with ab initio downfolding for simulating strongly-correlated materials on quantum computers
• Persistence of charge ordering instability to Coulomb engineering in the excitonic insulator candidate TiSe${}_2$
• Ultrafast pseudomagnetic fields from electron-nuclear quantum geometry
• Machine learning model for efficient nonthermal tuning of the charge density wave in monolayer NbSe${}_2$
• Theory of ab initio downfolding with arbitrary range electron-phonon coupling