Introducing fluctuation-driven order into density functional theory using the quantum order-by-disorder framework

TL;DR

This paper introduces a method to incorporate fluctuation-driven electronic order into density functional theory using the quantum order-by-disorder framework, enabling first-principles calculations of collective electronic phenomena.

Contribution

It develops a self-consistent approach to include fluctuation-driven order in DFT by modifying the exchange-correlation functional with quantum order-by-disorder, applicable to superconductivity and spin nematic order.

Findings

Demonstrated the method on fluctuation-driven superconductivity

Applied the approach to spin nematic order

Provided implementation schemes for practical calculations

Abstract

Density functional theory in the local or semi-local density approximation is a powerful tool for materials simulation, yet it struggles in many cases to describe collective electronic order that is driven by electronic interactions. In this work it is shown how arbitrary, fluctuation-driven electronic order may be introduced into density functional theory using the quantum order-by-disorder framework. This is a method of calculating the free energy correction due to collective spin and charge fluctuations about a state that hosts static order, in a self-consistent manner. In practical terms, the quantum order-by-disorder method is applied to the Kohn-Sham auxiliary system of density functional theory to give an order-dependent correction to the exchange-correlation functional. Calculation of fluctuation propagators within density functional theory renders the result fully first-principles. Two types of order are considered as examples -- fluctuation-driven superconductivity and spin nematic order -- and implementation schemes are presented in each case.