EPR G TENSOR OF FREE RADICALS THEORY

自旋哈密顿参数的理论计算是非常困难的。 它不仅适用于结构测定， 识别生物系统中的自由基。 我们尤其 最感兴趣的是预测g张量的值，因为 g-张量是从以下获得的主要信息： 高频EPR 详细介绍了 g-张量与结构的根，结构可以是 阐明，不同的自由基可以区分，和溶剂 效果衡量。 使用半经验MO方法（AM 1和PM 3），我们可以 使超精细和g张量非常好的近似。 这些 计算主要受限于基集 决定了自旋密度分布。 在大多数情况下 自旋密度是相当准确地确定这种半经验 方法，但也有许多例外，特别是sigma 自由基和某些非平面π自由基。 更明确的结果 可以从从头计算中获得。 由于大 数量C。I.对于扩展基集生成的状态，我们是 目前仅限于小分子。 利用微扰方法，我们 计划将g张量计算扩展到大分子。 这是 一个正在进行的项目。

Theoretical calculations of spin-Hamiltonian parameters are very useful not only in determination of structure but also in the identification of radicals in biological systems. In particular, we are most interested in predicting values of the g-tensor, since the g-tensor is the primary piece of information obtained from high-frequency EPR. With detailed information on variation of the g-tensor with structure of the radical, the structure can be elucidated, different radicals can be distinguished, and solvent effects gauged. With semi-empirical MO methods (AM1 and PM3), we can make very good approximations of the hyperfine and g-tensors. These calculations are primarily limited by how well the basis set determines the spin-density distribution. In most cases the spin-density is determined fairly accurately by such semi-empirical methods, but there are also many exceptions, particularly sigma radicals and certain non-planar pi radicals. More definitive results can be obtained from ab ini tio calculations. Because of the large number of C. I. states generated for extended basis sets, we are currently limited to small molecules. Using perturbation methods, we plan to extend our g-tensor calculations to large molecules. This is an ongoing project.