Rusakov Yury Yu, Rusakova Irina L, Krivdin Leonid B
Siberian Branch of the Russian Academy of Sciences, A. E. Favorsky Irkutsk Institute of Chemistry, Favorsky St 1, Irkutsk, 664033, Russia.
Magn Reson Chem. 2015 Jul;53(7):485-92. doi: 10.1002/mrc.4226. Epub 2015 May 21.
The main factors affecting the accuracy and computational cost of the Second-order Möller-Plesset perturbation theory (MP2) calculation of (77) Se NMR chemical shifts (methods and basis sets, relativistic corrections, and solvent effects) are addressed with a special emphasis on relativistic effects. For the latter, paramagnetic contribution (390-466 ppm) dominates over diamagnetic term (192-198 ppm) resulting in a total shielding relativistic correction of about 230-260 ppm (some 15% of the total values of selenium absolute shielding constants). Diamagnetic term is practically constant, while paramagnetic contribution spans over 70-80 ppm. In the (77) Se NMR chemical shifts scale, relativistic corrections are about 20-30 ppm (some 5% of the total values of selenium chemical shifts). Solvent effects evaluated within the polarizable continuum solvation model are of the same order of magnitude as relativistic corrections (about 5%). For the practical calculations of (77) Se NMR chemical shifts of the medium-sized organoselenium compounds, the most efficient computational protocols employing relativistic Dyall's basis sets and taking into account relativistic and solvent corrections are suggested. The best result is characterized by a mean absolute error of 17 ppm for the span of (77) Se NMR chemical shifts reaching 2500 ppm resulting in a mean absolute percentage error of 0.7%.
研究了影响二阶莫勒-普列塞特微扰理论（MP2）计算（77）Se核磁共振化学位移的准确性和计算成本的主要因素（方法和基组、相对论校正和溶剂效应），特别强调了相对论效应。对于后者，顺磁贡献（390 - 466 ppm）比抗磁项（192 - 198 ppm）占主导地位，导致总屏蔽相对论校正约为230 - 260 ppm（约占硒绝对屏蔽常数总值的15%）。抗磁项实际上是恒定的，而顺磁贡献跨度为70 - 80 ppm。在（77）Se核磁共振化学位移尺度上，相对论校正约为20 - 30 ppm（约占硒化学位移总值的5%）。在可极化连续介质溶剂化模型中评估的溶剂效应与相对论校正具有相同的数量级（约5%）。对于中等大小有机硒化合物的（77）Se核磁共振化学位移的实际计算，建议采用相对论迪尔基组并考虑相对论和溶剂校正的最有效计算方案。最佳结果的特征是（77）Se核磁共振化学位移跨度达2500 ppm时平均绝对误差为17 ppm，平均绝对百分比误差为0.7%。
