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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >DFT-SQM Force Field for Nickel Porphine: Intrinsic Ruffling
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DFT-SQM Force Field for Nickel Porphine: Intrinsic Ruffling

机译：镍卟啉的DFT-SQM力场：内在波动

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Nonlocal density functional theory [DFT] has been used to compute vibrational frequencies and intensities of nickel porphine and of several isotopomers via a scaled quantum mechanical [SQM] force field [FF]. The results support and extend those obtained from a revised empirical FF. The force constants are similar for the two FF's, although the SQM FF has a complete set of off-diagonal elements. The SQM FF produces somewhat more accurate frequencies and isotope shifts than the empirical FF for the in-plane NiP modes. In addition, the SQM FF calculates out-of-plane modes that are in good agreement with available infrared [IR] data. Also, the SQM FF satisfactorily reproduces the relative intensities of both IR and [off-resonance] Raman bands. A striking result is the calculation of large Raman intensities for nontotally symmetric B_(1g) modes in conformity with experimental FT-Raman spectra. This effect is attributed to the phasing of local polarizability components of the pyrrole rings and methine bonds. The DFT-computed bond distances and angles are in good agreement with crystallographically determined values. The lowest energy structure is a true minimum with D_(2d) symmetry. It is slightly distorted from the planar geometry along the ruffling coordinate. Constraining it to be planar [D_(4h] raises the energy slightly [-0.1 kcal/mol] and leads to an imaginary frequency for the ruffling mode. This finding provides theoretical confirmation of Hoard's empirical observation that metal ions with M-N (pyrrole) bonds significantly shorter than 2.00 A produce an out-of-plane distortion of the macrocycle. The computed degree of ruffling is small, as are the calculated shifts in vibrational frequencies [< 6 cm~(-1)]. Although the symmetry lowering relaxes selection rules, the induced intensity in IR- or Raman forbidden modes is calculated to be negligible, except for a single IR band associated with an out-of-plane mode [E_g, 420 cm~(-1)], which is indeed observed experimentally. The agreement of both frequencies and intensities with experiment provides further validation of the accuracy of the DFT, ever for molecules as complex as metalloporphyrins.
机译：非局部密度泛函理论[DFT]已用于通过比例量子力学[SQM]力场[FF]计算镍卟啉和几种同分异构体的振动频率和强度。结果支持并扩展了从修订后的实证研究中获得的结果。尽管SQM FF具有完整的非对角线元素集，但两个FF的力常数相似。与面内NiP模式的经验FF相比，SQM FF产生的频率和同位素位移更为精确。另外，SQM FF计算出与可用红外[IR]数据高度吻合的面外模式。同样，SQM FF令人满意地再现了IR和[非共振]拉曼带的相对强度。引人注目的结果是，根据实验性FT-Raman光谱，计算了非完全对称B_（1g）模式的大拉曼强度。该效应归因于吡咯环和次甲基键的局部极化率分量的相变。 DFT计算的键距和角度与晶体学确定的值非常吻合。最低的能量结构是具有D_（2d）对称性的真最小值。它沿着波状坐标从平面几何形状略微变形。将其约束为平面[D_（4h）会稍微提高[-0.1 kcal / mol]的能量，并导致波动模式的假想频率，这一发现为Hoard的经验观察提供了理论证实，即金属离子具有MN（吡咯）键显着小于2.00 A会产生大循环的平面外失真，所计算出的波纹程度较小，所计算出的振动频率漂移也较小[<6 cm〜（-1）]。规则，在红外或拉曼禁忌模式下的感应强度被计算为可忽略不计，除了与平面外模式相关的单个红外波段[E_g，420 cm〜（-1）]，实际上是通过实验观察到的频率和强度与实验的一致性，为像金属卟啉这样复杂的分子提供了DFT准确性的进一步验证。

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