Vibrational averages along thermal lines

TL;DR

The paper introduces thermal lines, a new method that simplifies calculating vibrational averages of physical properties at finite temperatures, reducing sampling complexity significantly.

Contribution

It presents thermal lines as a novel approach to efficiently compute vibrational averages, enabling studies of larger systems and advanced methods.

Findings

Thermal lines reduce sampling points by up to tenfold.

Accurate vibrational averages obtained for diamond, silicon, and L-alanine.

Method applicable to complex systems and beyond semi-local DFT.

Abstract

A method is proposed for the calculation of vibrational quantum and thermal expectation values of physical properties from first principles. Thermal lines are introduced: these are lines in configuration space parametrized by temperature, such that the value of any physical property along them is approximately equal to the vibrational average of that property. The number of sampling points needed to explore the vibrational phase space is reduced by up to an order of magnitude when the full vibrational density is replaced by thermal lines. Calculations of the vibrational averages of several properties and systems are reported, namely the internal energy and the electronic band gap of diamond and silicon, and the chemical shielding tensor of L-alanine. Thermal lines pave the way for complex calculations of vibrational averages, including large systems and methods beyond semi-local density functional theory.