Setting and analysis of the multi-configuration time-dependent Hartree-Fock equations

TL;DR

This paper formulates and analyzes the Multi-Configuration Time-Dependent Hartree-Fock equations for molecular systems, establishing existence, uniqueness, and conditions for global solutions, with a focus on the invertibility of the density matrix.

Contribution

It introduces a new analysis framework for MCTDHF equations, proving existence, uniqueness, and global well-posedness under certain conditions, including the invertibility of the density matrix.

Findings

Existence and uniqueness of solutions under full-rank density matrix.

A sufficient energy condition for global invertibility of the density matrix.

Convergence of regularized solutions to the original system when invertibility holds.

Abstract

In this paper we motivate, formulate and analyze the Multi-Configuration Time-Dependent Hartree-Fock (MCTDHF) equations for molecular systems under Coulomb interaction. They consist in approximating the N-particle Schrodinger wavefunction by a (time-dependent) linear combination of (time-dependent) Slater determinants. The equations of motion express as a system of ordinary differential equations for the expansion coefficients coupled to nonlinear Schrodinger-type equations for mono-electronic wavefunctions. The invertibility of the one-body density matrix (full-rank hypothesis) plays a crucial role in the analysis. Under the full-rank assumption a fiber bundle structure shows up and produces unitary equivalence between convenient representations of the equations. We discuss and establish existence and uniqueness of maximal solutions to the Cauchy problem in the energy space as long as the density matrix is not singular. A sufficient condition in terms of the energy of the initial data ensuring the global-in-time invertibility is provided (first result in this direction). Regularizing the density matrix breaks down energy conservation, however a global well-posedness for this system in L^2 is obtained with Strichartz estimates. Eventually solutions to this regularized system are shown to converge to the original one on the time interval when the density matrix is invertible.