Towards Hybrid Density Functional Calculations of Molecular Crystals via Fragment-Based Methods

TL;DR

This paper develops and tests hybrid density functional methods embedded within each other for molecular crystals, achieving accurate lattice energies and cell volumes with reduced computational cost.

Contribution

It introduces two QM:QM schemes for molecular crystal calculations and compares their performance to traditional density functionals.

Findings

QM:QM schemes yield lattice energy errors comparable to hybrid functionals.

Cell volume errors of QM:QM are between GGA and hybrid functionals.

The methods reduce computational cost while maintaining accuracy.

Abstract

We introduce and employ two QM:QM schemes (a quantum mechanical method embedded into another quantum mechanical method) and report their performance for the X23 set of molecular crystals. We furthermore present the theory to calculate the stress tensors necessary for the computation of optimized cell volumes of molecular crystals and compare all results to those obtained with various density functionals and more approximate methods. Our QM:QM calculations with PBE0:PBE+D3, PBE0:PBE+MBD, and B3LYP:BLYP+D3 yield at a reduced computational cost lattice energy errors close to the ones of the parent hybrid density functional method, whereas for cell volumes, the errors of the QM:QM scheme methods are in between the GGA and hybrid functionals.