Software

We write our own computer codes for a wide variety of quantum chemistry, many-body, and other numerical methods needed to conduct our research. As a result, we maintain a rich and constantly improving local software infrastructure, especially in areas of ab initio electronic structure and nuclear structure theories.

We have recently started migrating some of our newest coupled-cluster (CC) approaches to GitHub. Among them is a PSI4 plugin, available here, which performs CC calculations with single, double, and triple excitations, treated fully, as in CCSDT, and with active orbitals, as in CCSDt, which can further be corrected using the CC(P;Q)-based CC(t;3) approach.

We are also responsible for all CC and equation-of-motion CC (EOMCC) options in the popular electronic structure package GΛMESS. This includes novel theories developed by our group, in addition to a variety of standard approaches. Among them are the triples as well as triples and quadruples corrections, in factorized and completely renormalized forms, to ground-state CCSD energies (e.g., CR-CC(2,3)), the completely renormalized triples corrections to excited-state EOMCCSD energies, such as δ-CR-EOMCC(2,3) or δ-CR-EOMCCSD(T), the electron-attached and ionized EOMCC methods, EA- and IP-EOMCC, respectively, through 3p-2h/3h-2p terms treated fully and using active orbitals, the aforementioned CC(t;3) corrections to CCSDt (plus CCSDt and CCSDT as byproducts), and local, linear-scaling cluster-in-molecule (CIM) CC approaches, from CCSD through CCSD(T) to CR-CC(2,3), and their sublinear-scaling multi-level CIM extensions allowing one to mix different methods within a single calculation (e.g., MP2 and CCSD(T) or CR-CC(2,3)). Thus, we provide researchers at universities and national laboratories as well as instructors and students using GAMESS in education with the new computational chemistry tools that have not been available to them before. Some of our CC and EOMCC methods are also available in NWChem, MRCC, and Q-Chem.