Semiclassical (SC) methods for real-time quantum dynamics are rigorous, accurate and provide a frame-work in which nuclear motions, electronic state transitions, and even quantized electromagnetic field vari-ables can be treated on an even-footing. However, the cost of these more accurate ‘quantum-limit’ SC methods forbids their use in high-dimensional system studies, while the less accurate ‘classical-limit’ methods place constraints on the extent to which quantum effects can be captured. Fortunately, in practice, neither extreme is necessary: frequently a high-level quantum mechanical description is only required for a handful of modes, while the majority of ‘environment’ modes are well served with a lower level of theory. We have developed a novel mixed quantum-classical (MQC)-SC framework that employs the modified Filinov filtration scheme to selectively quantize a subset of system degrees of freedom without introducing adhoc interaction terms commonly used in fragment-based multiphysics methods. Using a range of model systems, we have demonstrated that these MQC-SC methods can capture quantum effects at a significantly reduced cost for linear operator correlation functions. Further, we have developed a modified MQC approach that is equally successful for non-linear operator correlation functions and can be used to quantify zero-pointenergy conservation. This talk will introduce our MQC-SC approach, highlight its favorable and unfavorable properties and conclude with a discussion of the path forward.

Many phases of Filinov filtration: Mixed-limit semiclassical dynamics

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