基于B3LYP/LanL2DZ和B3LYP/aug-cc-pVTZ方法计算铜络合物的铜同位素分馏

Calculation of copper isotope fractionation for copper complexes using quantum chemistry methods B3LYP/LanL2DZ and B3LYP/aug-cc-pVTZ

铜的氯络合物和硫氢络合物是铜在成矿流体中稳定存在并参与地球化学迁移的重要形式;文中利用量子化学方法B3LYP/LanL2DZ和B3LYP/aug-cc-pVTZ研究计算了Cu＋络合物（CuCl、[CuCl2]-、[CuCl3]2-、CuCl（H2O）（真空）、CuHS,0～600℃）和Cu2＋络合物（CuCl＋、CuCl2（真空）、CuOH＋、CuHS＋、Cu（HS）2,0～300℃）的简约配分函数比。然后对比前人的理论与计算成果,讨论了不同基组方法计算铜络合物的铜同位素分馏的适应性。计算结果表明：利用LanL2DZ得到的Cu＋氯络合物的分馏结果103lnβ65-63比应用其他方法计算的结果偏大;而基于LanL2DZ基组计算Cu2＋络合物的结果比aug-cc-pVTZ基组偏小。利用赝势基组LanL2DZ计算铜同位素分馏和实验结果偏差比较大,可能的原因是基于赝势基组LanL2DZ对上述络合物开展结构优化时,键长值比实验值偏大所致。因此,从理论计算上看,利用6-311＋G（d,p）基组可能更适合铜络合物的铜同位素分馏计算。虽然这些不同基组计算的结果存在差异,但与前人的实验结果相比,各种理论计算结果都在误差允许范围之内。鉴于此,在利用第一性原理计算同位素分馏系数时,如果计算条件允许,最好利用多种基组计算并作对比分析。

Copper chlorides and copper hydrosulfides are important complexes that exist stably and participate in geochemical migration in copper ore-forming fluids; we use quantum chemistry methods B3LYP/LanL2DZ and B3LYP/aug-cc-pVTZ to calculate the reduced partition function ratios of Cu＋ complexes （CuCl, [CuCl2]- , [CuCl3]2- , CuCI（H2O） （vacuo）, CullS, 0 - 600℃） and Cu2＋ complexes （CuCl＋ , CuCl2 （vacuo）, CuOH＋ ,CullS＋ ,Cu（HS）2, 0- 300℃）. We try to discuss which methods and basis sets are best suited for copper isotope fractionation of copper complexes compared to previous theoretical calculation results. Our results suggest that the fractionation values 103lnβ65-63 of Cu＋ chlorides complexes using I.anL2DZ basis set is larger than other methods, and, meanwhile, the results of Cu2＋ complexes calculated by LanL2DZ basis set is smaller than aug-cc-pVTZ basis set. There are larger deviation for calculating copper isotope fractionation between theoretical results by pseudo-potentials basis set LanL2DZ and experimental results; it may be due to optimized bond lengths being larger than experimental values when using LanL2DZ. Therefore, the basis set of 6-311＋G（d,p） may be more suitable for copper isotope fractionation. Although there are differences among different basis sets, all the calculated results are within the permitted error compared to experimental results. For these reasons, it is better to compare different basis sets if the conditions are available, when use the first principle theory to calculate isotope fractionation factors.