# Thermofield Theory for Finite-Temperature Quantum Chemistry

## TL;DR

This paper introduces a thermofield dynamics framework for finite-temperature quantum chemistry, enabling the development of thermal wave function methods and applying them to the Hubbard model with promising results.

## Contribution

It extends thermofield dynamics to quantum chemistry, proposing new finite-temperature correlated wave function methods and two approaches to imaginary time Schrödinger equations.

## Key findings

- Derived thermal configuration interaction theories
- Applied methods to the Hubbard model
- Compared results with exact benchmarks

## Abstract

Thermofield dynamics has proven to be a very useful theory in high-energy physics, particularly since it permits the treatment of both time- and temperature-dependence on an equal footing. We here show that it also has an excellent potential for studying thermal properties of electronic systems in physics and chemistry. We describe a general framework for constructing finite temperature correlated wave function methods typical of ground state methods. We then introduce two distinct approaches to the resulting imaginary time Schrodinger equation, which we refer to as fixed-reference and covariant methods. As an example, we derive the two corresponding versions of thermal configuration interaction theory, and apply them to the Hubbard model, while comparing with exact benchmark results.