Linear-scaling generation of potential energy surfaces using a double incremental expansion

TL;DR

This paper introduces a linear-scaling method for generating potential energy surfaces by combining incremental expansion with local coordinate transformations, enabling efficient vibrational analysis of large covalently bound systems.

Contribution

It presents a novel double incremental approach that combines n-mode expansion with local coordinate adaptation for efficient PES generation.

Findings

Achieves linear scaling in PES calculations.

Demonstrates fast convergence with respect to fragment number.

Introduces modest errors due to coordinate transformation.

Abstract

We present a combination of the incremental expansion of potential energy surfaces (PESs), known as n-mode expansion, with the incremental evaluation of the electronic energy in a many-body approach. The application of semi-local coordinates in this context allows the generation of PESs in a very cost-efficient way. For this, we employ the recently introduced flexible adaptation of local coordinates of nuclei (FALCON) coordinates. By introducing an additional transformation step, concerning only a fraction of the vibrational degrees of freedom, we can achieve linear scaling of the accumulated cost of the single point calculations required in the PES generation. Numerical examples of these double incremental approaches for oligo-phenyl examples show fast convergence with respect to the maximum number of simultaneously treated fragments and only a modest error introduced by the additional transformation step. The approach, presented here, represents a major step towards the applicability of vibrational wave function methods to sizable, covalently bound systems.