Dipartimento di Chimica dell'Università degli Studi di Modena, Via Campi 183, 41100 Modena, Italy.
J Phys Chem A. 2009 Dec 31;113(52):14465-79. doi: 10.1021/jp903859k.
Three-dimensional models of the quantum-mechanical current density induced by a uniform magnetic field in the electron cloud have been obtained for closed-shell systems BeH(-), BH, and CH(+), characterized by induced orbital paramagnetism, and in planar unsaturated hydrocarbons C(4)H(4) and clamped C(8)H(8), exhibiting pi paramagnetism. It is shown that, even for these paramagnetic systems, the paramagnetic contributions to magnetic susceptibilities and nuclear magnetic shielding, customarily taken into account in perturbation theory approaches, can formally be eliminated via the procedure of continuous transformation of the origin of the current density-paramagnetic zero. The definition of magnetic response properties can therefore be recast as a sum of two formally "diamagnetic" terms for any molecule, including systems showing strong induced orbital paramagnetism. It is shown that the paramagnetism in the compounds studied arises from the nodal topology of the electronic wave function. In particular, paratropic vortices circulate about stagnation lines at the intersection of nodal surfaces of the highest-occupied zero-order molecular orbital and corresponding first-order orbital.
已为具有诱导轨道顺磁性的闭壳层体系 BeH(-)、BH 和 CH(+)，以及表现出π顺磁性的平面不饱和烃 C(4)H(4)和夹钳 C(8)H(8)，获得了在电子云内均匀磁场诱导的量子力学电流密度的三维模型。结果表明，即使对于这些顺磁体系，通常在微扰理论方法中考虑的对磁化率和核磁共振屏蔽的顺磁贡献，可以通过电流密度-顺磁零点的连续变换过程正式消除。因此，对于任何分子，包括表现出强诱导轨道顺磁性的体系，磁响应性质的定义都可以重新表述为两个形式上“抗磁性”项的和。结果表明，所研究化合物中的顺磁性源于电子波函数的节点拓扑结构。特别是，围绕在最高占据零阶分子轨道和相应的一阶轨道的节点面的交点处的静止线上，会出现反磁涡旋。
