Variational Discrete Action Theory

Here we propose the variational discrete action theory (VDAT) to study ground state properties of quantum many-body Hamiltonians. VDAT is a based on sequential product density matrix (SPD) ansatz, characterized by an integer $\mathcal{N}$, which monotonically approaches exact solution with increasing $\mathcal{N}$. To evaluate SPD, introduce and corresponding time Green's function. We use exactly SPD in two canonical models interacting electrons: Anderson impurity model $d=\ensuremath{\infty}$ Hubbard model. For latter, $\mathcal{N}=2--4$, where $\mathcal{N}=2$ recovers Gutzwiller approximation (GA), show that $\mathcal{N}=3$, evaluates Gutzwiller-Baeriswyl wave function, provides truly minimal yet precise description Mott physics cost similar GA. flexible for studying Hamiltonians, competing both state-of-the-art methods simple, efficient all within single framework.