Questaal is a suite of electronic structure programs.Recent development work includes Dynamic Mean Field Theory (DMFT-QSGW), the Bethe Salpeter Equation (BSE), and direct (Green Function) solution of the Dirac equation.

These codes share a basis set of atom-centred functions. The basis has its genesis in the Linear Muffin Tin Orbitals (LMTO) method of O. K. Andersen, who formulated the theory of linear methods in band theory.

What is interesting for me is the Ladder diagram capability for W. This program has two interesting capabilities.

W+BSE:  To include ladders in W, the RPA W is first calculated in hx0fp0 and this is then used in the Bethe-Salpeter equation (BSE) for the full polarization matrix. Tutorial. Theory.

QSGW + DMFT: When localised electronic orbitals (d- or f- type) participate in the states near the fermi level, the effect of electronic correlation can not be included as a small perturbation (RPA) and more accurate methods have to be invoked. The Questaal code has been interfaced with the Continuous Time Quantum Monte Carlo solver developed by K. Haule and coworkers. This couples the QSGW description of the lattice with state-of-the-art Dynamical Mean Field Theory approaches. This code requires that Haule’s CTQMC be installed. The interface to that code is lmfdmft.