rPM6 parameters for phosphorous and sulphur-containing open-shell molecules

ABSTRACT

In this article, we have introduced a reparameterisation of PM6 (rPM6) for phosphorus and sulphur to achieve a better description of open-shell species containing the two elements. Two sets of the parameters have been optimised separately using our training sets. The performance of the spin-unrestricted rPM6 (UrPM6) method with the optimised parameters is evaluated against 14 radical species, which contain either phosphorus or sulphur atom, comparing with the original UPM6 and the spin-unrestricted density functional theory (UDFT) methods. The standard UPM6 calculations fail to describe the adiabatic singlet-triplet energy gaps correctly, and may cause significant structural mismatches with UDFT-optimised geometries. Leaving aside three difficult cases, tests on 11 open-shell molecules strongly indicate the superior performance of UrPM6, which provides much better agreement with the results of UDFT methods for geometric and electronic properties.

KEYWORDS:

• Open-shell
• sulphur
• phosphorus
• PM6

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Japan Society for the Promotion of Science (JSPS) KAKENHI Grant-in-Aid for Young Scientists (B)(grant number JP16K17856), JSPS KAKENHI Grant-in-Aid for Scientific Reasearch (C)(grant number JP15KT0143 and JP16K07325), by CREST JST (grant number JPMJCR14M3), and the Ministry of Education, Culture, Sports, Science and Technology Grant-in-Aid for Scientific Research on Innovation Areas "3D Active-Site Science'' [grant number JP26105012].