# Comscope Software Packages

### LQSGW: Ab initio electronic structure code

Our parallel ab initio electronic structure code, LQSGW, lies at the heart of Comsuite, as it is a basic building block for the theoretical calculation of material properties. Calculation of electronic structure can be understood mathematically as an eigenvalue problem in which the determination of the electron self-energy matrix Σ is the main challenge. LQSGW offers several levels of approximations to Σ: LDA, Hartree-Fock, self-consistent GW, and linearized quasiparticle GW. These approaches allow one to study the electronic structure, i.e., the ground and excited state electronic properties, of weakly to moderately correlated materials. One can study the properties of strongly correlated materials by combining these approaches with DMFT or the Gutzwiller approximation.

### ComDMFT

ComDMFT is a parallel ab initio software package combining the LQSGW code with the massively parallel ComCTQMC DMFT solver. It can perform either self-consistent DFT+DMFT or self-consistent qsGW+DMFT. In either case the the non-local physics is calculated by LQSGW and the local strong correlation physics is calculated using DMFT. ComDMFT chooses the local orbitals of the atoms by optimizing maximally localized Wannier orbitals, using the Wannier90 code. In the qsGW+DMFT option ComDMFT calculates the Hubbard U interaction strength using the cRPA approximation, while in the DFT+DMFT option this strength is chosen by the user.

ComRISB is distributed with ComDMFT; it is available both in ComDMFT and as a standalone package.

### ComCTQMC

DMFT calculations of electronic structure require one to solve an effective quantum impurity problem. ComCTQMC is a quantum Monte Carlo solver for the DMFT impurity problem, and is designed to be used by DMFT codes and cluster DMFT codes. It is currently the only open source CTQMC (continuous time quantum Monte Carlo) code which features GPU acceleration. It also implements the worm algorithm which allows unrestricted measurement of multi-particle and multi-time correlation functions. ComCTQMC can utilize all computing resources – both CPUs and GPUs – on a leadership class supercomputing facility.

### CyGUTZ

CyGUTZ is an efficient Gutzwiller solver which solves a generic tight-binding model with local interactions using the Gutzwiller approximation (the rotationally invariant slave-boson method). The Gutzwiller approximation is an alternative to DMFT. For calculations of realistic materials, it has interfaces with WIEN2k and with ComRISB. CyGUTZ can solve the Gutzwiller approximation much faster than any solver can solve an equivalent DMFT problem, and it can represent the zero-temperature correlated physics without any trouble, which is not the case in DMFT.

### ComRISB

The ComRISB software package integrates LQSGW with CyGUTZ and with Wannier90, allowing CyGUTZ to compute strongly correlated physics and LQSGW to calculate weakly correlated physics. ComRISB can perform both self-consistent DFT+Gutzwiller and one-shot qsGW+Gutzwiller calculations. ComRISB provides a much faster method for investigating the ground state of correlated materials than methods using DMFT.

### Gutzwiller_MD

Gutzwiller_MD is a contribution from Gia-Wei Chern, a member of the Comscope community who is working on using the the Gutzwiller approximation to do molecular dynamics on strongly interacting materials. Gutzwiller_MD is a proof of principle of Gutzwiller-assisted molecular dynamics in an interacting toy model system.

### EDRIXS

EDRIXS is a toolkit for the simulations of resonant inelastic x-ray scattering (RIXS) and x-ray absorption (XAS) spectra of strongly correlated materials based on exact diagonalization of certain model Hamiltonians. At Comscope, it is used to interpret RIXS spectra of d-electron materials obtained at the Soft Inelastic X-ray (SIX) beamline at NSLS-II.