**************************************************************************
   **************************************************************************
   **                                                                      **
   **   /$$      /$$ /$$$$$$  /$$$$$$ /$$$$$$$                  /$$        ** 
   **  | $$$    /$$$/$$__  $$/$$__  $| $$__  $$                | $$        **
   **  | $$$$  /$$$| $$  \ $| $$  \__| $$  \ $$/$$$$$$  /$$$$$$| $$   /$$  ** 
   **  | $$ $$/$$ $| $$  | $| $$     | $$$$$$$|____  $$/$$_____| $$  /$$/  **
   **  | $$  $$$| $| $$  | $| $$     | $$____/ /$$$$$$| $$     | $$$$$$/   **
   **  | $$\  $ | $| $$/$$ $| $$    $| $$     /$$__  $| $$     | $$_  $$   **
   **  | $$ \/  | $|  $$$$$$|  $$$$$$| $$    |  $$$$$$|  $$$$$$| $$ \  $$  **
   **  |__/     |__/\____ $$$\______/|__/     \_______/\_______|__/  \__/  **
   **          \__/                                                        **
   **                                                                      **
   **                 The Merced Quantum Chemistry Package                 **
   **                              (MQCPack)                               **
   **                            Version 26.8.0                            **
   **                            August 3, 2026                            **
   **                                                                      **
   **                                                                      **
   ** Written By:                                                          **
   **    Lee M. Thompson, Xianghai Sheng, Andrew D. Mahler, Dave Mullally  **
   **    and Hrant P. Hratchian                                            **
   **                                                                      **
   **                                                                      **
   **************************************************************************
   **************************************************************************

The MQC package is a library containing objects and procedures to streamline develoments of quantum chemical methodologies. MQC is built using object-orientated Fortran and has three key features.

1. Algebra

MQC has a number of mathematical objects that are designed to hide away and automate manipulation of arrays. Arrays can be packed for efficient memory use and used for operations completely transparently to the user. Furthermore, there is no need to type arrays, as this can be manipulated on the fly. Arrays carry their own procedures, and use underlying lapack routines for efficiency. See the documentation for more information, but as an example:

scalar = vector%pop()   

removes the value from the end of a vector and returns it to scalar,

call matrix%eigensystem(metric,eigenvalues,rightvectors)  

computes the generalized eigenequation of the matrix given the metric matrix and returns the eigenvalues and the right eigenvectors (you can return the left eigenvectors as well if you wish, or just the left eigenvectors, or neither set of eigenvectors). MQC can deal with integer, real and complex arrays.

2. Quantum chemistry

MQC has objects that built over algebra objects designed specifically for quantum chemistry calculations. The most developed set of objects are the EST objects. This can work out whether you have a restricted, unrestricted or general spin framework and store the spin blocks as makes sense, it can automatically determine how to multiply different objects or carry out manipulations. Procedure interfaces allow you to use these objects just like normal matrices or take advantage of their higher-level organization.

3. Interfacing with QM codes

A key feature of MQC is that it makes interacting with a range of computational chemistry codes entirely seamless. By having interfaces with different code APIs, MQC is able to fill the quantum chemistry objects and pass them back out in a manner that is completely transparent to the user. Thus, regardless regardles of what your favorite software is, your program will work without any modifications.

Getting Started

Prerequisites

• Required Software:
  • autotools (only for developers)
  • BLAS
  • LAPACK library
    • gcc v8 or newer
    • gfortran v8 or newer, or pgfortran v19 or newer
• Optional Software:
  • gauopen
  • Gaussian 16 or higher

Installing

The interactive installer remains available:

./mqc_install

Enable MatrixFile support with the external GauOpen source directory and the currently supported 8-byte integer ABI. The build compiles the unmodified qcmatrix.F and qcmatrixio.F files directly with isolated legacy-source flags. Configure identifies the supported public or frontier GauOpen API from the selected sources:

./configure --prefix=/path/to/install \
  --with-gauopen=/path/to/gauopen \
  --with-gauopen-integer-bytes=8
make MQC_LAPACK="-llapack" MQC_BLAS="-lblas"
make check MQC_LAPACK="-llapack" MQC_BLAS="-lblas"
make install MQC_LAPACK="-llapack" MQC_BLAS="-lblas"

The default --with-gauopen-api=auto can be replaced by --with-gauopen-api=public or --with-gauopen-api=frontier after verifying the source interface. Public GauOpen supports numerical MatrixFile records but does not provide character-record routines; MQCPack character FAF operations therefore terminate with an explicit unsupported-feature diagnostic. Frontier GauOpen provides the TypeA and character-buffer interface used for character scalar and fixed-width-vector FAF records. To prevent positive TypeA records from being silently treated as integers, the public profile also rejects frontier version-3 FAF files.

Use --without-gauopen for a FormChk-only configuration; that path does not need the GauOpen sources and produces a library that can link and use the MQC_Gaussian formatted-checkpoint interface. MatrixFile types remain available at compile time for shared source compatibility, but a MatrixFile operation reports that GauOpen support was not configured and terminates. A Git checkout may need autoreconf --install once to generate configure; release source archives normally include generated Autotools files.

Licence

This project is licensed under the Apache License - see the LICENSE file for details