Calculations of Potential Energy Surfaces Using Monte Carlo Configuration Interaction

TL;DR

This paper demonstrates that Monte Carlo configuration interaction (MCCI) can efficiently approximate ground-state potential energy surfaces of small molecules and larger systems, achieving good accuracy with a small fraction of the full configuration interaction space.

Contribution

The study applies MCCI to compute potential energy curves, showing it can provide accurate results with significantly reduced computational effort compared to FCI.

Findings

MCCI yields accurate potential energy curves with minimal FCI space.

MCCI performs well on small molecules and ethylene, but less accurately on large hydrogen lattices.

Potential energy curves are often more accurate than single-point energies.

Abstract

We apply the method of Monte Carlo configuration interaction (MCCI) to calculate ground-state potential energy curves for a range of small molecules and compare the results with full configuration interaction. We show that the MCCI potential energy curve can be calculated to relatively good accuracy, as quantified using the non-parallelity error, using only a very small fraction of the FCI space. In most cases the potential curve is of better accuracy than its constituent single-point energies. We finally test the MCCI program on systems with basis sets beyond full configuration interaction: a lattice of fifty hydrogen atoms and ethylene. The results for ethylene agree fairly well with other computational work while for the lattice of fifty hydrogens we find that the fraction of the full configuration interaction space we were able to consider appears to be too small as, although some qualitative features are reproduced, the potential curve is less accurate.