Department of Chemistry, University of Basel, Klingelbergstrasse 80, 4056 Basel, Switzerland.
J Phys Chem A. 2009 Nov 26;113(47):13199-209. doi: 10.1021/jp903954t.
Atomic multipole moments are used to investigate vibrational frequency shifts of CO and H(2) in uniform and inhomogeneous electric fields using ab initio calculations and Molecular Dynamics (MD) simulations. The importance of using atomic multipole moments that can accurately represent both molecular electrostatics and the vibrational response of the molecule to changes in the local electric field is highlighted. The vibrational response of CO to applied uniform and inhomogeneous electric fields is examined using Density Functional Theory calculations for a range of test fields, and the results are used to assess the performance of different atomic multipole models. In uniform fields, the calculated Stark tuning rates of Deltamu = 0.52 cm(-1)/(MV/cm) (DFT), Deltamu = 0.55 cm(-1)/(MV/cm) (fluctuating three-point charge model), and Deltamu = 0.64 cm(-1)/(MV/cm) (Multipole model up to octupole), compare favorably with the experimentally measured value of 0.67 cm(-1)/(MV/cm). For H(2), which has no permanent dipole moment, CCSD(T) calculations demonstrate the importance of bond-weakening effects in force fields in response to the applied inhomogeneous electric field. Finally, CO in hexagonal ice is considered as a test system to highlight the performance of selected multipolar models in MD simulations. The approach discussed here can be applied to calibrate a range of multipolar charge models for diatomic probes, with applications to interpret Stark spectroscopy measurements in protein active sites.
原子多极矩用于研究 CO 和 H2 在均匀和非均匀电场中的振动频率位移，使用从头算计算和分子动力学（MD）模拟。强调了使用原子多极矩的重要性，原子多极矩可以准确地表示分子静电和分子对局部电场变化的振动响应。使用密度泛函理论计算对一系列测试场进行 CO 对施加的均匀和非均匀电场的振动响应研究，并使用结果评估不同原子多极模型的性能。在均匀场中，计算出的 Stark 调谐率为 Deltamu = 0.52 cm-1/(MV/cm)（DFT），Deltamu = 0.55 cm-1/(MV/cm)（波动三点电荷模型），Deltamu = 0.64 cm-1/(MV/cm)（多极模型高达八极），与实验测量值 0.67 cm-1/(MV/cm) 相当。对于没有永久偶极矩的 H2，CCSD(T)计算证明了力场中键弱化效应在响应施加的非均匀电场中的重要性。最后，考虑了六方冰中的 CO 作为测试系统，以突出选定多极模型在 MD 模拟中的性能。这里讨论的方法可以应用于校准一系列双原子探针的多极电荷模型，以应用于解释蛋白质活性位点中的 Stark 光谱测量。
