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An ab initio study of nuclear volume effects for isotope fractionations using two‐component relativistic methods
Author(s) -
Nemoto Keisuke,
Abe Minori,
Seino Junji,
Hada Masahiko
Publication year - 2015
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.23858
Subject(s) - component (thermodynamics) , ab initio , isotope , volume (thermodynamics) , chemistry , relativistic quantum chemistry , computational chemistry , physics , nuclear physics , thermodynamics , organic chemistry
We investigate the accuracy of two‐component Douglas–Kroll–Hess (DKH) methods in calculations of the nuclear volume term (≡ lnK nv ) in the isotope fractionation coefficient. lnK nv is a main term in the chemical equilibrium constant for isotope exchange reactions in heavy element. Previous work based on the four‐component method reasonably reproduced experimental lnK nv values of uranium isotope exchange. In this work, we compared uranium reaction lnK nv values obtained from the two‐component and four‐component methods. We find that both higher‐order relativistic interactions and spin‐orbit interactions are essential for quantitative description of lnK nv . The best alternative is the infinite‐order Douglas–Kroll–Hess method with infinite‐order spin‐orbit interactions for the one‐electron term and atomic‐mean‐field spin‐same‐orbit interaction for the two‐electron term (IODKH‐IOSO‐MFSO). This approach provides almost equivalent results for the four‐component method, while being 30 times faster. The IODKH‐IOSO‐MFSO methodology should pave the way toward computing larger and more general molecules beyond the four‐component method limits. © 2015 Wiley Periodicals, Inc.