Glycine valence orbital electron densities: Comparison of electron momentum spectroscopy experiments with Hartree-Fock and density functional theories
Glycine valence orbital electron densities: Comparison of electron momentum spectroscopy experiments with Hartree-Fock and density functional theories
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DOI：
10.1021/ja9613015
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发表时间：
1996-10-30
影响因子：
15
通讯作者：
Brion, CE
中科院分区：
文献类型：
--
作者：
Neville, JJ;Zheng, Y;Brion, CE
实验动量分布（轨道图像）对应于气态甘氨酸的外层价层中的电子密度分布已通过在6-27 eV的结合能范围内在1200 eV +结合能的冲击能量下进行的电子动量谱测量获得。实验数据进行了比较与理论动量分布计算使用Hartree-Fock和Kohn-Sham密度泛函理论。计算的动量分布对应于预测在165摄氏度的实验温度下存在的五种主要构象的玻尔兹曼加权和。基组的大小和灵活性的重要性进行了调查的情况下，Hartree-Fock的结果进行计算，使用一系列的基组范围从最小（STO-3G）的近Hartree-Fock限制（aug-cc-pVTZ）。密度泛函理论计算的交换相关势能泛函的类型的敏感性进行了研究，通过比较使用局部密度近似与那些由贝克，Perdew，李，杨和帕尔提出的非局部泛函得到的结果。据发现，实验结果一般是最好的模拟密度泛函理论计算，只有很小的差异，注意到使用不同的势能泛函得到的结果之间。在Hartree-Fock计算的情况下，增加基组大小超过6-311++C** 基组的基组大小对计算的动量分布没有明显的影响，与实验动量分布相比，计算的动量分布倾向于低估低电子动量值的强度，特别是对于甘氨酸的最外层价轨道。这表明，电子相关效应的考虑是必要的正确建模的化学敏感的外部空间区域的甘氨酸的外层价轨道的电子密度。
Experimental momentum profiles (orbital images) corresponding to the electron density distribution in the outer valence shell of gaseous glycine have been obtained by electron momentum spectroscopy measurements conducted over the binding energy range of 6-27 eV at an impact energy of 1200 eV + binding energy. The experimental data are compared with theoretical momentum profiles calculated using Hartree-Fock and Kohn-Sham density functional theories. The calculated momentum profiles correspond to a Boltzmann weighted sum of the five dominant conformers predicted to be present at the experimental temperature of 165 degrees C. The importance of basis set size and flexibility is investigated in the case of the Hartree-Fock results by performing calculations using a series of basis sets ranging from minimal (STO-3G) to the near-Hartree-Fock limit (aug-cc-pVTZ). The sensitivity of the density functional theory calculations to the type of exchange-correlation potential energy functional is investigated by comparing results using the local density approximation with those obtained with nonlocal functionals proposed by Becke, Perdew, and Lee, Yang, and Parr. It is found that the experimental results are generally best modeled by the density functional theory calculations, with only small differences noted among the results obtained using the different potential energy functionals. In the case of the Hartree-Fock calculations, increasing the basis set size beyond that of the 6-311++C** basis set has no discernible effect on the calculated momentum profiles, which in comparison to the experimental momentum profiles tend to underestimate the intensity at low values of electron momentum, particularly for the outermost valence orbitals of glycine. This suggests that a consideration of electron correlation effects is necessary for correct modeling of the chemically sensitive outer spatial regions of the electron density of the outer valence orbitals of glycine.