Tyndall National Institute, University College Cork, Dyke Parade, Lee Maltings, Cork, Ireland.
Quantum Theory Project, 2234 New Physics Building #92, PO Box 118435, University of Florida at Gainesville, Gainesville, Florida 32611-8435, USA.
J Chem Phys. 2014 Feb 28;140(8):084114. doi: 10.1063/1.4866609.
Dissociation energies for the diatomic molecules C2, N2, O2, CO, and NO are estimated using the Monte Carlo configuration interaction (MCCI) and augmented by a second order perturbation theory correction. The calculations are performed using the correlation consistent polarized valence "triple zeta" atomic orbital basis and resulting dissociation energies are compared to coupled cluster calculations including up to triple excitations (CCSDT) and Full Configuration Interaction Quantum Monte Carlo (FCIQMC) estimates. It is found that the MCCI method readily describes the correct behavior for dissociation for the diatomics even when capturing only a relatively small fraction (∼80%) of the correlation energy. At this level only a small number of configurations, typically O(10(3)) from a FCI space of dimension O(10(14)), are required to describe dissociation. Including the perturbation correction to the MCCI estimates, the difference in dissociation energies with respect to CCSDT ranges between 1.2 and 3.1 kcal/mol, and the difference when comparing to FCIQMC estimates narrows to between 0.5 and 1.9 kcal/mol. Discussions on MCCI's ability to recover static and dynamic correlations and on the form of correlations in the electronic configuration space are presented.
使用蒙特卡罗组态相互作用（MCCI）并通过二阶微扰理论修正来估计双原子分子 C2、N2、O2、CO 和 NO 的离解能。计算使用相关一致极化价“三重 zeta”原子轨道基，并将得到的离解能与包括三重激发（CCSDT）和全组态相互作用量子蒙特卡罗（FCIQMC）估计在内的耦合簇计算进行比较。结果表明，即使仅捕获相关能的相对较小部分（约 80％），MCCI 方法也能很好地描述双原子的离解正确行为。在这个水平上，只需从维度 O(10(14))的 FCI 空间中通常为 O(10(3))的少数配置即可描述离解。对于 MCCI 估计值，包括微扰修正，与 CCSDT 的离解能差异在 1.2 到 3.1 kcal/mol 之间，与 FCIQMC 估计值的差异缩小到 0.5 到 1.9 kcal/mol 之间。讨论了 MCCI 恢复静态和动态相关的能力以及电子组态空间中相关的形式。
