Department of Biology and Chemistry, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong.
J Chem Phys. 2010 Sep 21;133(11):114304. doi: 10.1063/1.3479759.
The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D(0)) and heats of formation at 0 K (ΔH(o)(f0)) and 298 K (ΔH(o)(f298)) for NiC and NiC(+) are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC(+) to be (1)∑(+) and (2)∑(+), respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D(0)(Ni-C)-D(0)(Ni(+)-C). The analysis of the correction terms shows that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of NiC/NiC(+). For the experimental D(0) and ΔH(o)(f0) values of NiC/NiC(+), which are not known experimentally, we recommend the CCSDTQ(Full)/CBS predictions [D(0)(Ni-C)=4.048 eV, D(0)(Ni(+)-C)=3.360 eV, ΔH(o)(f0)(NiC)=749.0 kJ/mol, and ΔH(o)(f0)(NiC(+))=1555.1 kJ/mol].
镍碳化合物的电离能 (IE) 以及镍碳化合物和镍碳化合物正离子在 0 K 时的键离解能 (D(0)) 和生成焓 (ΔH(o)(f0)) 以及 298 K 时的生成焓 (ΔH(o)(f298)) 是通过基于波函数的 CCSDTQ(Full)/CBS 方法和多参考组态相互作用 (MRCI) 方法与戴维森修正 (MRCI+Q) 预测的。这里呈现的 CCSDTQ(Full)/CBS 计算涉及到在耦合簇水平上达到完全四重激发以及零点振动能 (ZPVE)、高阶相关、核心价电子 (CV)、自旋轨道耦合 (SO) 和标量相对论效应 (SR) 修正的完整基组 (CBS) 极限的近似值。目前的计算为 NiC 和 NiC(+) 的基态提供了正确的对称预测，分别为 (1)∑(+) 和 (2)∑(+)。CCSDTQ(Full)/CBS IE(NiC)=8.356 eV 被发现与实验 IE 值 8.372 05±0.000 06 eV 非常吻合。在 MRCI+Q/cc-pwCV5Z 水平上，包括 ZPVE、SO 和 SR 效应的预测 IE(NiC)值为 8.00 eV，比实验值低 0.37 eV。这项工作与之前的实验和理论研究一起支持了这样的结论，即 CCSDTQ(Full)/CBS 方法能够为 3d 过渡金属碳化物（如 FeC 和 NiC）提供可靠的 IE 预测。此外，CCSDTQ(Full)/CBS 计算给出了 D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV 的预测值，这也与实验测定值 0.732 21±0.000 06 eV 一致，而 MRCI+Q 计算（具有相对论和 CV 效应）则预测 D(0)(Ni-C)-D(0)(Ni(+)-C)的低值为 0.39 eV。对校正项的分析表明，CV 和价态价电子相关超出 CCSD(T) 波函数以及相对论效应对 NiC/NiC(+)的计算热化学性质有显著贡献。对于 NiC/NiC(+)的实验 D(0)和 ΔH(o)(f0) 值，我们建议使用 CCSDTQ(Full)/CBS 预测值 [D(0)(Ni-C)=4.048 eV，D(0)(Ni(+)-C)=3.360 eV，ΔH(o)(f0)(NiC)=749.0 kJ/mol，以及 ΔH(o)(f0)(NiC(+))=1555.1 kJ/mol]。
