MolSSI Integral Reference Project
MolSSI Integral Reference Project Documentation


The MolSSI Integral Reference Project (MIRP) is a project overseen by the Molecular Sciences Software Institute (MolSSI). Its primary goal is to create and maintain reference implementations for integrals commonly found in quantum chemistry software.

MIRP has two main parts. The first is the reference implementations themselves. These implementations are generally slow algorithms, however they tend to be simple and easier to understand than algorithms typically found in production. In addition, the reference implementation is also written using both the usual double-precision floating point numbers, as well as using an arbitrary-precision interval arithmetic library (arblib - This library allows for estimation of the amount of error (such as roundoff error) accumulated throughout the computation.

The second part of MIRP is a set of precomputed values that new and existing integral packages can test against to detect deficiencies in their algorithms. These values are computed using the functionality described above. Due to the use of the interval arithmetic library, the value of the integrals can be computed to a given target precision and ensured to be accurate to the last printed place (unit of least precision, ulp).

Source Code

The source code of MIRP is available at GitHub at

MIRP (and dependencies) can be built with most standard C/C++ compilers. In addition, both MIRP (and the dependencies) can be obtained as linux executables and shared libraries.

Source, Binary, and Reference File Archives

Archives of source and binaries, as well as reference data files, can be found on Zenodo.

Software (source and binaries):

Reference data:

These represent DOIs for the overall project and always point to the latest release. If you are using a specific version, you should specify the DOI for that version.

Main Documentation

Integrals and Algorithms

MIRP Technical Details


Some examples of using MIRP can be found in the examples subdirectory. Examples include using MIRP as a library, as well as how to read from a reference file.

Reporting Bugs, Issues, and Improvements

Bugs and suggestions for improvements can be reported via github issues or by emailing the main author directly.


MIRP is primarily written by Benjamin Pritchard <bpp4@.nosp@m.vt.e.nosp@m.du>, a Software Scientist at MolSSI.


MIRP is released under the 3-Clause BSD License. See the LICENSE file for more details.


This work was supported by the Molecular Sciences Software Institute under U.S. National Science Foundation grant ACI-1547580.