First principle calculations of effective exchange integrals: Comparison between SR (BS) and MR computational results

Kizashi Yamaguchi, Satomichi Nishihara, Toru Saito, Shusuke Yamanaka, Yasutaka Kitagawa, Takashi Kawakami, Satoru Yamada, Hiroshi Isobe, Mitsutaka Okumura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

First principle calculations of effective exchange integrals (J) in the Heisenberg model for diradical species were performed by both symmetry-adapted (SA) multi-reference (MR) and broken-symmetry (BS) single reference (SR) methods. Mukherjee-type (Mk) state specific (SS) MR coupled-cluster (CC) calculations by the use of natural orbital (NO) references of ROHF, UHF, UDFT and CASSCF solutions were carried out to elucidate J values for di-and poly-radical species. Spin-unrestricted Hartree Fock (UHF) based coupled-cluster (CC) computations were also performed to these species. Comparison between UHF-NO(UNO)-MkMRCC and BS UHF-CC computational results indicated that spin-contamination of UHF-CC solutions still remains at the SD level. In order to eliminate the spin contamination, approximate spin-projection (AP) scheme was applied for UCC, and the AP procedure indeed corrected the error to yield good agreement with MkMRCC in energy. The CC double with spin-unrestricted Brueckner's orbital (UBD) was furthermore employed for these species, showing that spin-contamination involved in UHF solutions is largely suppressed, and therefore AP scheme for UBCCD removed easily the rest of spin-contamination. We also performed spin-unrestricted pure-and hybrid-density functional theory (UDFT) calculations of diradical and polyradical species. Three different computational schemes for total spin angular momentums were examined for the AP correction of the hybrid (H) UDFT. HUDFT calculations followed by AP, HUDFT(AP), yielded the S-T gaps that were qualitatively in good agreement with those of MkMRCCSD, UHF-CC(AP) and UB-CC(AP). Thus a systematic comparison among MkMRCCSD, UCC(AP) UBD(AP) and UDFT(AP) was performed concerning with the first principle calculations of J values in di-and poly-radical species. It was found that BS (AP) methods reproduce MkMRCCSD results, indicating their applicability to large exchange coupled systems.

Original languageEnglish
Title of host publicationProceedings of the International Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010
EditorsTheodore E. Simos, Theodore E. Simos, George Maroulis, Theodore E. Simos, Theodore E. Simos
PublisherAmerican Institute of Physics Inc.
Pages15-29
Number of pages15
ISBN (Electronic)9780735412828
DOIs
Publication statusPublished - Jan 1 2015
Externally publishedYes
EventInternational Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010 - Psalidi, Kos, Greece
Duration: Oct 3 2010Oct 8 2010

Publication series

NameAIP Conference Proceedings
Volume1642
ISSN (Print)0094-243X
ISSN (Electronic)1551-7616

Conference

ConferenceInternational Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010
CountryGreece
CityPsalidi, Kos
Period10/3/1010/8/10

Keywords

  • Approximate spin projection (AP) method
  • Mukherjee's MRCC theory (MkMRCC)
  • Polyradical systems
  • Spin contamination
  • UHF natural orbital (UNO) based MkMRCC

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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    Yamaguchi, K., Nishihara, S., Saito, T., Yamanaka, S., Kitagawa, Y., Kawakami, T., Yamada, S., Isobe, H., & Okumura, M. (2015). First principle calculations of effective exchange integrals: Comparison between SR (BS) and MR computational results. In T. E. Simos, T. E. Simos, G. Maroulis, T. E. Simos, & T. E. Simos (Eds.), Proceedings of the International Conference of Computational Methods in Sciences and Engineering 2010, ICCMSE 2010 (pp. 15-29). [4906626] (AIP Conference Proceedings; Vol. 1642). American Institute of Physics Inc.. https://doi.org/10.1063/1.4906626