### Abstract

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.

Original language | English |
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Pages (from-to) | 816-820 |

Number of pages | 5 |

Journal | Journal of Computational Chemistry |

Volume | 36 |

Issue number | 11 |

DOIs | |

Publication status | Published - 2015 Apr 30 |

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### Keywords

- isotope fractionation
- nuclear volume effect
- relativistic quantum chemistry
- two-component theory
- uranium

### ASJC Scopus subject areas

- Chemistry(all)
- Computational Mathematics

### Cite this

*Journal of Computational Chemistry*,

*36*(11), 816-820. https://doi.org/10.1002/jcc.23858