..
    : PyBEST: Pythonic Black-box Electronic Structure Tool
    : Copyright (C) 2016-- The PyBEST Development Team
    :
    : This file is part of PyBEST.
    :
    : PyBEST is free software; you can redistribute it and/or
    : modify it under the terms of the GNU General Public License
    : as published by the Free Software Foundation; either version 3
    : of the License, or (at your option) any later version.
    :
    : PyBEST is distributed in the hope that it will be useful,
    : but WITHOUT ANY WARRANTY; without even the implied warranty of
    : MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
    : GNU General Public License for more details.
    :
    : You should have received a copy of the GNU General Public License
    : along with this program; if not, see <http://www.gnu.org/licenses/>
    :
    : --

.. _intro_pybest_overview:

PyBEST Overview
################

Our Proclamation
================

PyBEST is a *Py*\ thonic *B*\ lack-box *E*\ lectronic *S*\ tructure *T*\ ool,
written primarily in the `Python programming language <https://www.python.org/>`_
with additional parts written in C++ (interfaced using `pybind11 <https://pybind11.readthedocs.io/en/stable/>`_)
and Fortran (interfaced using f2py).

PyBEST is a fully-fledged modern electronic-structure software package, developed at 
`NCU in Torun <https://www.umk.pl/en//>`_, 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 <http://pybest.fizyka.umk.pl/>`_.
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 |release|), follow the link `download PyBEST`_.

.. _download PyBEST: http://pybest.fizyka.umk.pl/downloads/pybest.v1.0.2.tar.gz
   

Main Features
=============

**Compatibility**

* Integrating the `LibInt2 <https://github.com/evaleev/libint>`_
  [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 <https://github.com/evaleev/libint>`_ [valeev2019]_

    * 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

* 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)

    * Coupled Cluster Singles and Doubles (CCSD)

* 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

**Post-Processing**

* Orbital entanglement and correlation analysis

    * for a pCCD reference function

* Orbital localization

    * Pipek-Mezey orbital localization

* Property calculations

    * Electric dipole moments


To be released soon
===================

**Hamiltonians**

* DKH (2nd and higher order)

* nARE/X2C

* Relativistic effective core potentials

**Electronic Structure Methods**

* EOM-LCCSD

* EOM-pCCD-LCCSD