柔性DM-NRG代码手册
Manual for the Flexible DM-NRG code
摘要：
量子杂质模型描述了一些局部自由度和非相互作用的费米子或玻色子态的连续体之间的相互作用。量子杂质模型的研究是理解更复杂的强关联系统的起点，但量子杂质模型也提供了各种相关介观结构，生物和化学过程，原子物理学的描述，并描述了耗散或退相等现象。这些模型的原型是安德森杂质模型，或单通道和多通道近藤模型。Wilson在70年代中期提出的数值重整化群方法（NRG）作为处理量子杂质问题的最精确和最有力的方法之一，长期以来一直以其原始形式被使用。最近，一些新的发展发生：首先，谱和守恒的密度矩阵NRG方法（DM-NRG）已经开发，这也被推广到非阿贝尔对称。在本手册中，我们介绍了NRG方法的一些基本概念，并介绍了最近开发的灵活DM-NRG代码。该代码使用用户定义的非阿贝尔对称动态，计算谱函数，期望值的本地运营商的用户定义的杂质模型。该代码还可以使用均匀的状态密度以及用户定义的状态密度。当前版本的代码假设费米子浴，它使用任何数量的U（1），SU（2）电荷SU（2）或Z（2）对称性。灵活的DM-NRG代码可从http://www.phy.bme.hu/~dmnrg下载
英文摘要：
Quantum impurity models describe interactions between some local degrees of freedom and a continuum of non-interacting fermionic or bosonic states. The investigation of quantum impurity models is a starting point towards the understanding of more complex strongly correlated systems, but quantum impurity models also provide the description of various correlated mesoscopic structures, biological and chemical processes, atomic physics and describe phenomena such as dissipation or dephasing. Prototypes of these models are the Anderson impurity model, or the single- and multi-channel Kondo models. The numerical renormalization group method (NRG) proposed by Wilson in mid 70's has been used in its original form for a longtime as one of the most accurate and powerful methods to deal with quatum impurity problems. Recently, a number of new developments took place: First, a spectral sum-conserving density matrix NRG approach (DM-NRG) has been developed, which has also been generalized for non-Abelian symmetries. In this manual we introduce some of the basic concepts of the NRG method and present recently developed Flexible DM-NRG code. This code uses user-defined non-Abelian symmetries dynamically, computes spectral functions, expectation values of local operators for user-defined impurity models. The code can also use a uniform density of states as well as a user-defined density of states. The current version of the code assumes fermionic bath's and it uses any number of U(1), SU(2) charge SU(2) or Z(2) symmetries. The Flexible DM-NRG code can be downloaded from http://www.phy.bme.hu/~dmnrg
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