论文标题
改善了具有较大活跃空间的相关系统的随机多驱动理论
Improved Stochastic Multireference Perturbation Theory for Correlated Systems with Large Active Spaces
论文作者
论文摘要
我们确定了最近引入的随机和内部收缩的FCIQMC-NEVPT2方法中的主要计算成本，用于大型活动空间尺寸。这是由于对低兴奋水平采样的决定因素对产生的四体中间体的贡献。我们开发了一种有效的方法来通过在所需的NEVPT2中间体的采样中通过额外的随机步骤来减轻这一成本。我们发现这种系统改进的附加采样可以将模拟时间缩短80 \％，而不会引入可观的错误。对于较大的活动空间，预计这种节省将增加。我们首次将这种增强的采样方案与完整的随机轨道优化相结合，并将其应用于（24,24）活性空间内的碳纤维蛋白系统的自旋状态，并使用相对微弱的计算资源找到FCIQMC-NEVPT2能量。现在，这种主动空间大小可以被视为在这种改进的随机方法中强烈相关的分子系统的NEVPT2计算的常规方法。
We identify the dominant computational cost within the recently introduced stochastic and internally contracted FCIQMC-NEVPT2 method for large active space sizes. This arises from the contribution to the four-body intermediates arising from low-excitation level sampled determinant pairs. We develop an effective way to mitigate this cost via an additional stochastic step within the sampling of the required NEVPT2 intermediates. We find this systematically improvable additional sampling can reduce simulation time by 80\% without introducing appreciable error. This saving is expected to increase for larger active spaces. We combine this enhanced sampling scheme with full stochastic orbital optimization for the first time, and apply it to find FCIQMC-NEVPT2 energies for spin states of an iron porphyrin system within (24,24) active spaces with relatively meagre computational resources. This active space size can now be considered as routine for NEVPT2 calculations of strongly correlated molecular systems within this improved stochastic methodology.
