Interactions and phonons derived from first principles using quantum Monte Carlo techniques

There are many systems which possess strong interactions and lattice degrees of freedom including high-temperature superconductors [1] and color centers in semiconductors [2]. However, electron-phonon models are typically derived within the framework of band structure, which leads to double-counting issues when interactions are re-introduced, among other issues of accuracy.

 

We investigate a new approach to deriving models that inherently includes one-body, two-body, and lattice terms from first principles quantum Monte Carlo (QMC) calculations [3]. This approach is based on scalable correlated electron calculations, and it offers high accuracy while avoiding double-counting. We assess this QMC downfolding approach on a series of well-characterized small molecules, comparing the spectra and Franck-Condon factors against the equation of motion coupled cluster method and experiments.

 

[1] Z.-X. Shen, et. al., Philos. Mag. B 82 1349-1368 (2002).

[2] M. Bockstedte, et. al., npj Quant. Mater. 3 31 (2018).

[3] H. Zheng, et. al., Front. Phys. 6 43 (2018).