PSI (computational chemistry)

PSI is an ab initio computational chemistry package originally written by the research group of Henry F. Schaefer, III (University of Georgia). It performs high-accuracy quantum computations on small to medium-sized molecules.

PSI3 is the latest release of the program package - it is open source, released as free under the GPL through SourceForge. Primary development is currently conducted by Daniel Crawford (Virginia Tech), David Sherrill (Georgia Tech), Edward Valeev (Virginia Tech), and Rollin King (Bethel University).

Features
The basic capabilities of PSI are concentrated around the following methods of quantum chemistry:


 * Hartree-Fock
 * Coupled cluster
 * CASSCF
 * multi-reference configuration interaction methods.

Several methods are available for computing excited electronic states, including configuration interaction singles (CIS), the random phase approximation (RPA), and equation-of-motion coupled cluster (EOM-CCSD). PSI3 also includes the explicitly-correlated MP2-R12 method and the ability to compute the Born-Oppenheimer diagonal correction using configuration interaction wavefunctions.