PSI3: An open‐source Ab Initio electronic structure package

Abstract

PSI3 is a program system and development platform for ab initio molecular electronic structure computations.The package includes mature programming interfaces for parsing user input, accessing commonly used data such as basis-set information or molecular orbital coefficients, and retrieving and storing binary data (with no software limitations on file sizes or file-system-sizes), especially multi-index quantities such as electron repulsion integrals. This platform is useful for the rapid implementation of both standard quantum chemical methods, as well as the development of new models. Features that have already been implemented include Hartree-Fock, multiconfigurational self-consistentfield, second-order Møller-Plesset perturbation theory, coupled cluster, and configuration interaction wave functions. Distinctive capabilities include the ability to employ Gaussian basis functions with arbitrary angular momentum levels; linear R12 second-order perturbation theory; coupled cluster frequency-dependent response properties, including dipole polarizabilities and optical rotation; and diagonal Born-Oppenheimer corrections with correlated wave functions. This article describes the programming infrastructure and main features of the package. PSI3 is available free of charge through the open-source, GNU General Public License.

Simulation and visualization of attosecond stimulated x-ray Raman spectroscopy signals in trans-N-methylacetamide at the nitrogen and oxygen K-edges

“…The ECA calculations were carried on using GAUSSIAN03, while the STEX calculations were implemented using PSI3. 39 All transition frequencies and dipole moments were calculated at the HF/6-311G** level. The ECA and STEX frontier orbital energies are compared in Table I (Table II) for core electronic excitation from N1s(O1s) orbital.…”

Equation of Motion Theory for Excited States in Variational Monte Carlo and the Jastrow Antisymmetric Geminal Power in Hilbert Space

“…EOM-CCSD, Davidsoncorrected MRCI (MRCI+Q) and FCI results were computed with MOLPRO [25], CIS results with QChem [26], and JAGP results with our own prototype Hilbert space quantum Monte Carlo code with one-and two-electron integrals imported from Psi3 [27]. In JAGP, we worked exclusively in the symmetrically orthogonalized S −1/2 orbital basis and froze the C, N and O 1s orbitals at the RHF level.…”

Core hole screening and decay rates of double core ionized first row hydrides

“…21 The Hartree-Fock calculations and the transformation of two electron integrals were performed using a modified PSI3 quantum package. 22 For the CI calculation we used a slightly different truncation scheme than that in Ref. 14.…”