Molecular Cluster Perturbation Theory. I. Formalism

TL;DR

This paper introduces MCPT(2), a scalable molecular cluster perturbation theory that explicitly calculates large systems' wavefunctions, demonstrated on solid hydrogen fluoride with up to 1,000 molecules.

Contribution

The paper develops a second-order molecular cluster perturbation theory with linear scaling and explicit wavefunction calculation, enabling large system simulations without periodic boundary conditions.

Findings

Successfully computed properties for up to 1,000 HF molecules.

Achieved good agreement with literature for dipole moments and vibrational frequencies.

Demonstrated scalability and efficiency of the MCPT(2) method.

Abstract

We present second-order molecular cluster perturbation theory (MCPT(2)), a linear scaling methodology to calculate arbitrarily large systems with explicit calculation of individual wavefunctions in a coupled-cluster framework. This new MCPT(2) framework uses coupled-cluster perturbation theory and an expansion in terms of molecular dimer interactions to obtain molecular wavefunctions that are infinite-order in both the electronic fluctuation operator and all possible dimer (and products of dimers) interactions. The MCPT(2) framework has been implemented in the new SIA/Aces4 parallel architecture, making use of the advanced dynamic memory control and fine grained parallelism to perform very large explicit molecular cluster calculations. To illustrate the power of this method, we have computed energy shifts, lattice site dipole moments, and harmonic vibrational frequencies via explicit calculation of the bulk system for the polar and non-polar polymorphs of solid hydrogen fluoride. The explicit lattice size (without using any periodic boundary conditions) was expanded up to 1,000 HF molecules, with 32,000 basis functions and 10,000 electrons. Our obtained HF lattice site dipole moments and harmonic vibrational frequencies agree well with the existing literature.