## Software

Programs targeted at users of electronic structure theory:

- Molpro: Most of our programs are distributed via the Molpro quantum chemistry package
- IboView: IboView is a program for chemical analysis and visualization of electronic structure. It is targeted at computational chemists and interested organic and inorganic chemists. See http://www.iboview.org

Some smaller programs, aimed at developers and researchers in electronic structure theory, are made available on this site:

#### f95rr: Random rounding numerical stability analysis

See separate homepage.

`f95rr` is a practical program for analyzing large programs (e.g., electronic structure packages) with respect to numerical stability. It can be used to obtain precise estimates of the number of digits which can be trusted, or to track down sources of instability, without major modifications of the main program.

#### fci: Full Configuration Interaction Impurity solver

Download here (version: 2013-10-02).

`fci` is a simple, stand-alone determinant-full configuration interaction program, which can be used as impurity solver for DMET or for electronic structure experiments. It supports spin-adapted Hamiltonians and symmetry-broken Hamiltonians (UHF). Details are provided in the README file.

#### ir/wmme: Basis functions & integrals

Download here (version: 2018-05-18).

Download here (version: 2014-10-30).

This program calculates a molecular Hamiltonian: You give it a molecuar geometry and a basis set name (or an explicit basis declaration), and it writes one- and two-electron integrals to disk. An interface for direct use in python is provided, as is an example code (`rhf_in_python.py`) showing how to use it for implementing a simple Hartree-Fock program.

#### ibo-ref: Reference implementation of the IAO/IBO techniques

Download here (version: 2014-10-30).

The program implements the intrinsic atomic orbitals as described in Intrinsic atomic orbitals: An unbiased bridge between quantum theory and chemical concepts J. Chem. Theory Comput., 9 4834 (2013) (*)

It is a python script; it first runs a Hartree-Fock calculation, and then constructs IAOs/IBOs and prints some basic data on partial charges and the molecular orbital composition. See enclosed README. This program requires ir/wmme in order to run (see above).

(*): Note: The published article has an error in the 2×2 update formulas for the localization functional with exponent 4 (in appendix D). Thanks to Andreas Köhn for pointing it out. The error was introduced in the production process and escaped detection during the proof corrections(**). The script and the published data always used the correct formulas. The correct formulas are also given in my last preprint, which can be downloaded here. (formalities: This document is the unedited Author’s version of a Submitted Work that was subsequently accepted for publication in the Journal of Chemical Theory and Computation, copyright (c)American Chemical Society after peer review. To access the final edited and published work see http://dx.doi.org/10.1021/ct400687b.).

(**): I think this was a very sneaky move of the error 8).

#### dmet_hyd: Molecular ab-initio version of the DMET approach

Download here (version: 2014-08-21). This program realizes the ab initio version of DMET for molecular model systems (in particular, hydrogen rings, chains, grids, etc). The theory is described in Density Matrix Embedding: A Strong-Coupling Quantum Embedding Theory J. Chem. Theory Comput. 9 1428 (2013) See enclosed readme file.

#### srci and cc-eqs-pv: Semi bi-orthogonal spin-free coupled cluster methods

Download srci (version: 2019-09-03).

Download cc-eqs-pv (version: 2019-09-03).

srci and cc-eqs-pv provide the reference implementation of spin-free higher-order coupled cluster methods (CC(2)–C(4)) presented in the article

Cong Wang, Gerald Knizia, “A simple permutation group approach to spin-free higher-order coupled-cluster methods” (1 May 2018)

- cc-eqs-pv: This is a python program which generates the non-redundant working equations for the spin-free higher order coupled cluster methods using permutation group techniques. It does so via the DECC-based second quantized algebra described in the paper, and tensor symmetry canonicalization with double-coset canonical representative techniques also described there. The code to compute the semi-bi-orthogonal projection matrices is also included.

- srci: This is a very simple coupled cluster/configuration interaction program which uses the equation files generated by cc-eqs-pv and evaluates CC(n) and CI(n) wave functions for concrete quantum chemical Hamiltonians. This is a proof-of-concept reference implementation.

See README files included in the respective packages for details.

#### renmol: Molecules & pictures

Download here (version: 2017-06-16).

This is a small python script used to make vector graphics of molecules, e.g.:

It is not bullet proof, but I think the pictures are pretty. Also, they are compact vector graphics (not bitmaps) and therefore infinitely scalable. Needs jmol to setup the viewing angle and asymptote to render the graphics. Both are available as packages with most linux distributions.

#### bethe_ansatz: Ground state properties of 1D Hubbard models

Download here (version: 2014-06-03).

This program can calculate a number of (exact) ground state properties of the infinite 1D Hubbard model, at arbitrary fillings (n) and couplings strengths (U), using the Bethe Ansatz solution.

Supported are energies/site, chemical potentials, metal-insulator transitions (1-particle gaps), and on-site spin correlation functions/particle number correlation functions.

Background: The 1D Hubbard model is one of the few exactly solvable model systems for strong correlation; this program computes reference data against which new electronic structure programs can be compared.

This program was made for Density matrix embedding: A simple alternative to dynamical mean-field theory, Phys. Rev. Lett. 109, 186404 (2012).