mixed-basis calculations based originally on QuEmb repository from oimeitei (https://github.com/oimeitei/quemb), and now later versions from quemb from troyvvgroup (https://github.com/troyvvgroup/quemb).
Allows for BE calculations to perfomed from a mixed-basis reference. Rather than using a single large-basis HF reference wavefunction, mixed-basis-be generates a set of BE(n)-in-BE(m) HF reference calculations with a dense-in-minimal basis set for a given BE(m) region. For sufficiently large systems, this reduces the time and memory costs for both the HF reference steps and the integral transformations to each integral space while preserving BE(n) accuracy. This allows for dense basis, large accuracy BE calculations to be performed for extended chemical systems.
To run the code, first install quemb using guide. Then, simply provide the geometry and charge of the system interest; size of big basis region, using the BE(x) prescription based on x connected coordination shells; chosen basis for the big (BE(m)) and small basis set regions; and BE(n) choice for BE fragment size. We provide an example shell script that passes this information to the python script interfacing with quemb. This script returns the correlation energy of the system, an estimation of the mixed HF energy, nuclear and core energies, and number of electrons. A crude chemical potential optimizer is added to optionally correct the number of electrons in the mixed calculations.
Please see our publication that describes the BE(n)-in-BE(m) mixed-basis method: 10.1021/acs.jctc.5c00241
@article{10.1021/acs.jctc.5c00241,
author = {Weisburn, Leah P. and Cho, Minsik and Bensberg, Moritz and Meitei, Oinam R. and Reiher, Markus and Van Voorhis, Troy},
title = {Multiscale Embedding for Quantum Computing},
year = {2025},
journal = {Journal of Chemical Theory and Computation},
website = {https://pubs.acs.org/doi/10.1021/acs.jctc.5c00241},
doi = {10.1021/acs.jctc.5c00241},
arxiv = {2409.06813},
}