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arXiv 1004.0740cond-mat.stat-mech
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Redfield方程的非平衡BBGKY族

Non-equilibrium BBGKY Hierarchy from the Redfield Equation

Jinshan Wu

摘要:

从非平衡Redfield方程出发,导出了BBGKY型的族系.进一步介绍了两个近似,每一个都可以用来截断和解决的层次。在第一近似中,这样的截断是通过将层次中的两粒子格林函数(GF)替换为它们在平衡时的值来执行的。第二种方法是基于团簇展开的方法,该方法从单粒子广义函数构造出双粒子广义函数,忽略了关联部分。一个非平衡威克定理被证明提供了一个基础,这种非平衡集群扩展。使用这两个近似,我们的方法求解Redfield方程,例如,一个N-位链的相互作用的无自旋费米子,涉及一个本征值问题的尺寸$2^{N}$和一个线性系统的尺寸$N^2$在第一种情况下,和一个非线性方程的尺寸$N^2$在第二种情况下,可以通过一系列的$N^2$线性系统迭代求解。其它当前可用的直接方法对应于线性系统或具有维度$4^N$的本征值系统加上具有维度$2^N$的本征值系统。作为一个测试的方法,对于尺寸N=4的小系统,结果被发现是一致的,与其他直接方法提供的结果。虽然这里没有讨论,但将这两种方法扩展到下一个级别是很简单的。这表明一个有前途的潜力,这种BBGKY样的方法的非平衡动力学方程。

英文摘要:

A BBGKY-like hierarchy is derived from the non-equilibrium Redfield equation. Two further approximations are introduced and each can be used to truncate and solve the hierarchy. In the first approximation such a truncation is performed by replacing two-particle Green's functions (GFs) in the hierarchy by their values at equilibrium. The second method is developed based on the cluster expansion, which constructs two-particle GFs from one-particle GFs and neglects the correlation part. A non-equilibrium Wick's Theorem is proved to provide a basis for this non-equilibrium cluster expansion. Using those two approximations, our method of solving the Redfield equation, for instance, of an N-site chain of interacting spinless fermions, involves an eigenvalue problem with dimension $2^{N}$ and a linear system with dimension $N^2$ in the first case, and a nonlinear equation with dimension $N^2$ in the second case, which can be solved iteratively via a sequence of $N^2$ linear systems. Other currently available direct methods correspond to a linear system or an eigenvalue system with dimension $4^N$ plus an eigenvalue system with dimension $2^N$. As a test of the methods, for small systems with size N=4, results are found to be consistent with results made available by other direct methods. Although not discussed here, extending both methods to their next levels is straightforward. This indicates a promising potential for this BBGKY-like approach of non-equilibrium kinetic equations.

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