CONTRIBUTION OF ELECTRON CORRELATION TO H-BONDS

氢键在化学和生物学中的重要性 引发了大量的调查。 我们目前了解的 这种键的基本性质在很大程度上取决于从头算 各种能量成分的分离。 但 以前的计算一般只限于SCF水平 因此忽略了电子相关的影响。 最近 研究提供了令人信服的证据，相关性起着重要的作用。 在氢键中起主要作用，贡献了很大一部分 结合能和显着影响其径向和角度 依赖 目前的建议旨在系统地 研究氢键中电子相关的影响， 它可以分解成色散能， 对一阶能量的相关校正（ 分子内相关性）。 前者将被计算 直接通过变分微扰理论和库仑部分 通过多极扩张的方式。 他们的总和将是 与超分子二阶多体相比 微扰理论（MP2），其中包含这两个条款，此外 他们的交换对手。 基础集将是双- 质量，增强了两套偏振功能， 设计用于最大化色散能量，最小化基组 叠加误差，准确再现实验 子系统的多极矩 数据将适合于 成对表达式以产生一组可传递的参数， 为了补充大的从头计算的目的， 仅限于SCF级别和用于合并的系统 转化为蒙特卡罗和动力学计算的势能。

The importance of the H-bond in chemistry and biology has motivated a great deal of inquiry. Our current understanding of the fundamental nature of this bond rests in large part on ab initio partitioning of the various energetic components. However, the previous calculations have generally been limited to the SCF level and have thus omitted the effects of electron correlation. Recent work has provided convincing evidence that correlation plays a major role in H-bonding, contributing a large fraction of the binding energy and significantly influencing its radial and angular dependence. The current proposal is designed to systematically investigate the effects of electron correlation in H-bonding, which may be broken down into dispersion energy and the correlation correction to the first-order energy (part of intramolecular correlation). The former will be calculated directly via variation-perturbation theory and the Coulomb part of the latter through a multipole expansion. Their sum will be compared with supermolecule second-order many body perturbation theory (MP2) which contains both terms in addition to their exchange counterparts. Basis sets will be of double- quality, augmented with two sets of polarization functions, designed to maximize dispersion energy, minimize basis set superposition error, and accurately reproduce experimental multipole moments of subsystems. The data will be fit to pairwise expressions to produce a set of transferrable parameters, for purposes of supplementation of ab initio calculations of large systems which are limited to the SCF level and for incorporation into potentials for Monte Carlo and dynamics calculations.