Overview

The in-medium similarity renormalization group (IMSRG) is a many-body method developed for low-energy nuclear structure. It was initiated by Scott Bogner, building off of the free-space SRG introduced by Bogner, Furnstahl, and Perry, in turn building off the initial work of Glazek and Wilson, and Wegner. Large-scale implementations for nuclear physics were developed by Koshiroh Tsukiyama, Heiko Hergert, Nathan Parzuchowski, Ragnar Stroberg, and Klaus Vobig (and probably others?). Titus Morris has made several theoretical contributions. The method is related to coupled cluster theory, especially unitary coupled cluster, and also to other developments in quantum chemistry.

The basic aim is to begin with a Hamiltonian describing a many-body system (primarily protons and neutrons in this code) and solve the non-relativistic Schrodinger equation. This is achieved by performing a unitary transformation on the Hamiltonian to bring it to a form more amenable to solving. The unitary transformation is parametrized by a "flow parameter" _s_, as _U(s)_ and we characterize it's _s_ dependence by specifying a generator eta. (Apparently it's not easy to typeset equations in this editor...)