# A variational approach to London dispersion interactions without density distortion

## TL;DR

This paper presents a variational wavefunction method that accurately models London dispersion interactions between neutral systems without altering their individual densities, enabling precise calculation of dispersion coefficients.

## Contribution

It introduces a novel variational approach that captures dispersion forces without density distortion, providing explicit formulas for dispersion coefficients based on ground-state pair densities.

## Key findings

- Accurately computes dispersion coefficients up to C10 for hydrogen atoms.
- Achieves errors below 0.2% in simple cases.
- Provides a theoretical framework for new approximation methods.

## Abstract

We introduce a class of variational wavefunctions that capture the long-range interaction between neutral systems (atoms and molecules) without changing the diagonal of the density matrix of each monomer. The corresponding energy optimization yields explicit expressions for the dispersion coefficients in terms of the ground-state pair densities of the isolated systems, providing a clean theoretical framework to build new approximations in several contexts. As the individual monomer densities are kept fixed, we can also unambiguously assess the effect of the density distortion on van der Waals interactions: for example, we obtain virtually exact dispersion coefficients between two hydrogen atoms up to $C_{10}$, and relative errors below $0.2\%$ in other simple cases.