The HEOM method is implemented in a number of freely available codes. A number of these are at the website of [[Yoshitaka Tanimura]] <ref>url=http://theochem.kuchem.kyoto-u.ac.jp/resarch/resarch08.htm</ref> including a version for GPUGPUs <ref name=Tsuchimoto>{{Citation | last = Tsuchimoto | first = Masashi |author2= Tanimura, Yoshitaka| year = 2015 | authorlink = Masashi Tsuchimoto | author2link = Yoshitaka Tanimura |title=Spins Dynamics in a Dissipative Environment: Hierarchal Equations of Motion Approach Using a Graphics Processing Unit (GPU) | journal = Journal of Chemical Theory and Computation | volume = 11 | issue = 7 | pages = 3859–3865| doi = 10.1021/acs.jctc.5b00488 | pmid = 26574467 }}</ref> which used improvements introduced inby theDavid thesisWilkins ofand David[[Nike WilkinsDattani]].<ref name=Wilkins>{{Citationcite journal | last last1=Wilkins |first1=David first |author2= DavidDattani, Nike| yearauthor2link = 2015Nike Dattani|title=Why authorlinkquantum =coherence Davidis M.not Wilkinsimportant |title=Ain Theoreticalthe InvestigationFenna-Matthews-Olsen IntoComplex Energy|journal=Journal Transferof InChemical PhotosyntheticTheory Openand QuantumComputation Systems |volume=11 arxiv|issue=7 |page=3411–3419 1503|url=https://doi.03277 org/10.1021/ct501066k}}</ref> The [[nanoHUB]] version provides a very flexible implementation.<ref>https://nanohub.org/resources/16106/relax</ref> An open source parallel CPU implementation is available from the [[Klaus Schulten|Schulten]] group.<ref>url=https://www.ks.uiuc.edu/Research/phi/</ref>
