1. PyBEST Overview

1.1. Our Proclamation

PyBEST is a Pythonic Black-box Electronic Structure Tool, written primarily in the Python programming language with additional parts written in C++ (interfaced using pybind11).

PyBEST is a fully-fledged modern electronic-structure software package, developed at NCU in Torun, released under the GNU General Public License. The package provides an efficient and reliable platform for electronic structure calculations at the interface of chemistry and physics using unique electronic structure methods. PyBEST is easy to use and easy to code in.

For more information, see our official homepage. You will also find there various versions of PyBEST to download and install including the most recent version of this documentation.

To download PyBEST (v 1.1.0), follow the link download PyBEST.

1.2. Main Features

Compatibility

  • Integrating the LibInt2 [valeev2019] library.

  • Adapting a modular structure to easily combine PyBEST with custom developments.

Electronic Structure Methods

  • Hamiltonians (various one- and two-electron integrals)

    • The electronic Schrodinger Hamiltonian in atom-centered Gaussian basis sets

      • One- and two-electron integrals computed with LibInt2 [valeev2019]

        • overlap, kinetic energy, nuclear, multipole, electron repulsion integrals (ERI)

      • pVp integrals

      • Cholesky-decomposed ERI

      • Douglas-Kroll-Hess Hamiltonian (DKH2)

    • Model Hamiltonians

      • 1-dimensional Hubbard model Hamiltonian (with and without periodic boundary conditions)

    • User-provided Hamiltonians

      • Molpro’s FCIDUMP format

  • Hartree-Fock theory:

    • Restricted and unrestricted orbitals

    • Various DIIS algorithms

  • Configuration Interaction methods

    • Configuration Interaction Singles (CIS)

    • Configuration Interaction Doubles (CID)

    • Configuration Interaction Singles and Doubles (CISD)

  • Coupled Cluster-type methods

    • pair-Coupled Cluster Doubles (pCCD), also known as the Antisymmetry Product of 1 reference-orbital Geminals (AP1roG)

    • Linearized Coupled Cluster Doubles (LCCD)

    • Linearized Coupled Cluster Singles and Doubles (LCCSD)

    • pCCD-LCCD (pCCD with an LCCD correction on top of it)

    • pCCD-LCCSD (pCCD with an LCCSD correction on top of it)

    • pCCD-CCS (pCCD with a Coupled Cluster Singles correction on top of it)

    • Coupled Cluster Doubles (CCD) in any restricted orbital basis

    • Coupled Cluster Singles and Doubles (CCSD) in any restricted orbital basis

    • Frozen-pair Coupled Cluster Doubles (fpCCD)

    • Frozen-pair Coupled Cluster Singles Doubles (fpCCSD)

    • Tailored Couples Cluster Singles Doubles (tCCSD)

  • Perturbation theory

    • Moller-Plesset Perturbation Theory of second order (MP2)

    • Symmetry Adapted Perturbation Theory (SAPT)

      • the SAPT0 un-coupled flavour for spin-restricted HF orbitals

    • Various Perturbation Theory models of second order with an pCCD reference function

      • PT2SDd (diagonal zero-order Hamiltonian, single determinant as dual state) with Doubles and Singles and Doubles

      • PT2MDd (diagonal zero-order Hamiltonian, pCCD as dual state) with Doubles and Singles and Doubles

      • PT2SDo (off-diagonal zero-order Hamiltonian, single determinant as dual state) with Doubles and Singles and Doubles

      • PT2MDo (off-diagonal zero-order Hamiltonian, pCCD as dual state) with Doubles and Singles and Doubles

      • PT2b (off-diagonal zero-order Hamiltonian, pCCD as dual state, full Hamiltonian as perturbation operator) with Doubles and Singles and Doubles including/excluding electron pairs

  • Equation of Motion Coupled Cluster methods

    • Equation of Motion CCS (EOM-CCS equivalent to CIS)

    • EOM-pCCD

    • EOM-pCCD+S (single excitation are included in the EOM ansatz only, while the CC ansatz is restricted to pCCD)

    • EOM-pCCD-CCS

    • EOM-LCCD

    • EOM-LCCSD

    • EOM-pCCD-LCCD

    • EOM-pCCD-LCCSD

Post-Processing

  • Orbital entanglement and correlation analysis

    • for a pCCD reference function

    • for a pCCD-LCC reference function

  • Orbital localization

    • Pipek-Mezey orbital localization

  • Property calculations

    • Electric dipole moments

1.3. To be released soon

Hamiltonians

  • nARE/X2C

  • Relativistic effective core potentials