Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000.
J Chem Theory Comput. 2012 Feb 14;8(2):598-609. doi: 10.1021/ct2008507. Epub 2012 Jan 27.
A method is reported by which calculated hyperfine coupling constants (HFCCs) and paramagnetic NMR (pNMR) chemical shifts can be analyzed in a chemically intuitive way by decomposition into contributions from localized molecular orbitals (LMOs). A new module for density functional calculations with nonhybrid functionals, global hybrids, and range-separated hybrids, utilizing the two-component relativistic zeroth-order regular approximation (ZORA), has been implemented in the parallel open-source NWChem quantum chemistry package. Benchmark results are reported for a test set of few-atom molecules with light and heavy elements. Finite nucleus effects on (199)Hg HFCCs are shown to be on the order of -11 to -15%. A proof of concept for the LMO analysis is provided for the metal and fluorine HFCCs of TiF3 and NpF6. Calculated pNMR chemical shifts are reported for the 2-methylphenyl-t-butylnitroxide radical and for five cyclopentadienyl (Cp) sandwich complexes with 3d metals. Nickelocene and vanadocene carbon pNMR shifts are analyzed in detail, demonstrating that the large carbon pNMR shifts calculated as +1540 for Ni (exptl.: +1514) and -443 for V (exptl.: -510) are caused by different spin-polarization mechanisms. For Ni, Cp to Ni π back-donation dominates the result, whereas for vanadocene, V to Cp σ donation with relaxation of the carbon 1s shells can be identified as the dominant mechanism.
报道了一种方法，通过将计算得到的超精细耦合常数（HFCC）和顺磁 NMR（pNMR）化学位移分解为局域分子轨道（LMO）的贡献，可以以化学直观的方式进行分析。在并行开源 NWChem 量子化学软件包中实现了一个新模块，用于带有非杂化泛函、全局杂化和范围分离杂化的密度泛函计算，利用了双分量相对论零阶正则逼近（ZORA）。报道了一组轻元素和重元素少原子分子的基准测试结果。结果表明，核有限效应对（199）Hg HFCC 的影响在-11 到-15%之间。为 TiF3 和 NpF6 的金属和氟 HFCC 提供了 LMO 分析的概念证明。报道了 2-甲基苯基叔丁基氮氧化物自由基和 5 个含 3d 金属的环戊二烯基（Cp）夹心配合物的计算 pNMR 化学位移。详细分析了镍烯和钒烯的碳 pNMR 位移，证明了计算得到的镍的大碳 pNMR 位移为+1540（实验值：+1514）和钒的-443（实验值：-510）是由不同的自旋极化机制引起的。对于镍，Cp 到 Ni π 反馈是主要机制，而对于钒烯，可以识别出 V 到 Cp σ 供体与碳 1s 壳层弛豫是主要机制。
