Parallel Monte Carlo Calculations of Condensed Quantum Systems

这是对正在进行的量子多体系统模拟研究的续期拨款。改进的技术和计算能力将使在几个更困难和复杂的问题上取得进展。详细研究了氦膜的结构和物相，量子化涡的结构和激发能，以及氦- 4非常接近融冻转变的流固相。一种新的费米子算法将应用于氦- 3的流体相研究，并将使用新的采样技术和改进的波函数改进先前对氦- 4的动量分布和凝聚分数的计算。一项新的研究将开始于液氦中氦- 3杂质的基态和激发态。我们将尝试构建一种基于硬核建模的量子力学软势问题的一般方法，并对二体势的其余部分采用合适的微扰方法。本文将发展模拟有限温度下量子系统的路径积分方法的形式化。正在进行的研究项目将集中于氦在液态和固态中的重要问题的计算模拟。这是一个困难和非常基本的问题，因为量子力学效应对这些系统来说并不小。为了处理这些计算密集型问题，新的计算机技术将得到发展。

This is a renewal grant for ongoing simulation studies of quantum many-body systems. Improved techniques and computing power will enable progress to be made on several more difficult and complex problems. Detailed studies will be made on the structure and phases of helium films, the structure and excitation energy of a quantized vortex, and the fluid and solid phases of helium-four very close to the melting-freezing transition. A new Fermion algorithm will be applied to study the fluid phase of helium-three and prior calculations on the momentum distribution and condensate fraction of helium-four will be improved using new sampling techniques and improved wave functions. A new study will be initiated on the ground and excited states of a helium-three impurity in liquid helium. An attempt will be made to construct a general approach to quantum mechanical soft potential problems based on hard-core modeling and a suitable perturbation approach to the remainder of the two-body potential. The formalism will be developed for the path integral method of simulating quantum systems at finite temperatures. %%% The ongoing research project will focus on the computational simulation of important problems concerning helium in its liquid and solid states. This is a difficult and very fundamental problem since quantum mechanical effects are not small for these systems. In order to deal with these computationally intensive problems, new computer techniques will be developed.