Quantum Monte Carlo calculations in the nuclear shell model by the complex Langevin method

TL;DR

This paper demonstrates that the complex Langevin method can effectively perform quantum Monte Carlo calculations in the nuclear shell model, overcoming the sign problem and providing accurate results for small systems at finite temperature.

Contribution

The study introduces the application of the complex Langevin method to nuclear shell model calculations, showing its potential as a complementary approach to variational methods.

Findings

Existence of a parameter region where CLM is valid

CLM reproduces exact diagonalization energy results

Potential for applying CLM to larger systems

Abstract

The nuclear shell model is known to describe the properties of various nuclei extremely well. However, the auxiliary-field quantum Monte Carlo calculations cannot be applied to it with general interactions due to the sign problem. The model has therefore been investigated primarily by variational methods, where the accuracy of the results depends crucially on the ansatz for the wave function. Here we perform the auxiliary-field quantum Monte Carlo calculations in the case of small systems at finite temperature using the complex Langevin method (CLM), which has been successfully applied to various interesting systems with the sign problem over the decade. In particular, we show the existence of a parameter region in which the validity criterion for the CLM is satisfied and the expectation value of the energy obtained by exact diagonalization is correctly reproduced. Thus the CLM can be a complementary approach to the variational method for large systems.