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，但这个方程对原子核的求解要比对电子的求解困难得多，结果是只有对小的气相分子才能从它那里得到精确的量子动力学。该项目旨在开发近似方法，使量子动力学能够在凝聚态系统中进行模拟，例如冰和液态水。关键思想是，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的量子效应的结果；实时量子相干基本上是平均的。该项目将建立在最近发展的混合量子统计-经典动力学方法称为“行星模型”，其中原子核的量子玻尔兹曼离域是通过一个补充的“行星”粒子来近似的，该粒子绕玻尔兹曼分布的质量中心的另一个粒子运行。该技术可以相对便宜地模拟红外光谱和中子散射截面等可观测特性，并在液态水红外光谱测试中给出了非常有希望的结果。本项目将重点扩展这种方法来处理非线性光谱。

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.