Quantum Nuclear Dynamics in the Condensed Phase

原子核的量子性质是由薛定谔方程决定的，但对于原子核来说，这个方程比电子更难解，因此只能对气相小分子进行精确的量子动力学计算。该项目旨在开发近似方法，使量子动力学能够在凝聚相系统中进行模拟，例如冰和液态水。其核心思想是，这种系统中的大多数量子效应(即零点能量和隧道效应)主要是玻尔兹曼统计中量子效应的结果；实时量子相干大多是平均的。这个项目将建立在最近开发的一种混合量子统计-经典动力学方法的基础上，该方法被称为‘行星模型’，根据该模型，原子核的量子Boltzmann离域是通过一个辅助的‘行星’粒子来近似的，该粒子绕另一个处于Boltzmann分布质量中心的粒子运行。这项技术可以相对廉价地模拟红外光谱和中子散射截面等可观测性质，并在液态水的红外光谱测试中给出了非常有希望的结果。这个项目的重点是将这一方法扩展到处理非线性光谱。

The quantum properties of nuclei are determined by the Schroedinger equation, but this equation is much more difficult to solve for nuclei than electrons, with the result that exact quantum dynamics can be obtained from it only for small gas-phase molecules. This project aims to develop approximate methods which will allow quantum dynamics to be simulated in condensed phase systems, such as ice and liquid water. The key idea is that most of the quantum effects in such systems (i.e. zero-point energy and tunnelling) are the result mainly of quantum effects in the Boltzmann statistics; real-time quantum coherences mostly average out. This project will build on a recently developed mixed quantum statistics-classical dynamics method knowns as the 'planetary model', whereby the quantum Boltzmann delocalisation of atomic nuclei is approximated by means of a supplementary 'planet' particle which orbits another particle at the centre of mass of the Boltzmann distribution. This technique allows observable properties such as infrared spectra and neutron-scattering cross sections to be simulated relatively cheaply, and has given very promising results in tests on the infrared spectra of liquid water. This project will focus on extending this methodology to treat non-linear spectra.