Explicitly correlated electronic structure calculations with transcorrelated matrix product operators

TL;DR

This paper introduces a novel implementation of the transcorrelated Hamiltonian within the DMRG framework, improving convergence in electronic structure calculations by explicitly incorporating electron-electron cusp conditions.

Contribution

It presents the first transcorrelated DMRG method using matrix product operators, handling non-Hermitian Hamiltonians and demonstrating improved basis set convergence.

Findings

Enhanced convergence to basis set limit compared to traditional DMRG.

Successful application to atoms and diatomic molecules.

Proposed extensions to reduce computational cost.

Abstract

In this work, we present the first implementation of the transcorrelated electronic Hamiltonian in an optimization procedure for matrix product states by the density matrix renormalization group (DMRG) algorithm. In the transcorrelation ansatz, the electronic Hamiltonian is similarity-transformed with a Jastrow factor to describe the cusp in the wave function at electron-electron coalescence. As a result, the wave function is easier to approximate accurately with the conventional expansion in terms of one-particle basis functions and Slater determinants. The transcorrelated Hamiltonian in first quantization comprises up to three-body interactions, which we deal with in the standard way by applying robust density fitting to two- and three-body integrals entering the second-quantized representation of this Hamiltonian. The lack of hermiticity of the transcorrelated Hamiltonian is taken care of along the lines of the first work on transcorrelated DMRG [J. Chem. Phys. 153, 164115 (2020)] by encoding it as a matrix product operator and optimizing the corresponding ground state wave function with imaginary-time time-dependent DMRG. We demonstrate our quantum chemical transcorrelated DMRG approach at the example of several atoms and first-row diatomic molecules. We show that transcorrelation improves the convergence rate to the complete basis set limit in comparison to conventional DMRG. Moreover, we study extensions of our approach that aim at reducing the cost of handling the matrix product operator representation of the transcorrelated Hamiltonian.