Shamov Grigory A, Schreckenbach Georg, Vo Thach N
Department of Chemistry, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
Chemistry. 2007;13(17):4932-47. doi: 10.1002/chem.200601244.
All the possible uranium(VI, V, IV) oxides, fluorides and oxofluorides were studied theoretically by using density functional theory (DFT) in the generalised gradient approximation (GGA), and three different relativistic methods (all-electron scalar four component Dyall RESC method (AE), relativistic small-core ECPs, and zeroth order regular approximation ZORA). In order to test different correlation methods, for the two former relativistic methods hybrid DFT, and, for the AE method, MP2 molecular orbital calculations were performed as well. Single-point AE-CCSD(T) energies were calculated on MP2 geometries as well. Energies of the uranium(VI) and (V) oxofluorides dissociation, uranium(VI) fluoride hydrolysis and oxofluoride disproportionation were calculated and compared against the available experimental thermochemical data. AE-CCSD(T) energies were the closest to the experiment. For GGA DFT methods, all the relativistic methods used yield similar results. For thermochemistry, the best quantitative agreement with the experimental and CCSD(T) values for both U=O and U-F bond strengths was obtained with hybrid DFT methods, provided that a reliable basis set was used. Both the GGA DFT and MP2 MO methods show overbinding of these bonds; moreover, this overbinding was found to be not uniform but strongly dependent on the coordination environment of the uranium atom in each case. U=O vibrational frequencies given by hybrid DFT, however, are systematically overestimated, and are better reproduced by GGA DFT; MP2 values usually fall in-between. Reaction enthalpies, U=O frequencies and complex geometries given by the PBE, MPBE, BPBE, BLYP and OLYP GGA functionals are quite similar, with OLYP performing slightly better than the others but still not as good as hybrid DFT. The geometries of the molecules are found to be influenced by the following factors: the inverse transinfluence (ITI) of the oxygen ligand and, for U(V), and U(IV), the Jahn-Teller distortion.
运用广义梯度近似（GGA）下的密度泛函理论（DFT）以及三种不同的相对论方法（全电子标量四分量Dyall RESC方法（AE）、相对论小核有效核势方法和零阶正则近似ZORA），对所有可能的铀（VI、V、IV）氧化物、氟化物和氟氧化物进行了理论研究。为了测试不同的关联方法，对于前两种相对论方法还进行了杂化DFT计算，对于AE方法则进行了MP2分子轨道计算。还在MP2几何构型上计算了单点AE - CCSD(T)能量。计算了铀（VI）和（V）氟氧化物的解离能、铀（VI）氟化物的水解能以及氟氧化物的歧化能，并与现有的实验热化学数据进行了比较。AE - CCSD(T)能量与实验值最为接近。对于GGA DFT方法，所使用的所有相对论方法都得出了相似的结果。对于热化学，使用杂化DFT方法，在使用可靠基组的情况下，对于U = O和U - F键强度，与实验值和CCSD(T)值取得了最佳的定量一致性。GGA DFT和MP2 MO方法都显示出这些键的过度结合；此外，发现这种过度结合并不均匀，而是在每种情况下都强烈依赖于铀原子的配位环境。然而，杂化DFT给出的U = O振动频率被系统地高估了，GGA DFT能更好地重现这些频率；MP2值通常介于两者之间。PBE、MPBE、BPBE、BLYP和OLYP GGA泛函给出的反应焓、U = O频率和配合物几何构型非常相似，其中OLYP的表现略优于其他泛函，但仍不如杂化DFT。发现分子的几何构型受以下因素影响：氧配体的反位效应（ITI），以及对于U(V)和U(IV)，姜 - 泰勒畸变。
