标题： 超导体的第一性原理理论中要再现的基本变量：粒子数的涨落 显示英文标题

标题： Basic variables to be reproduced in the first-principles theory for superconductors: Fluctuation of the particle number

摘要： 我们证明，二阶约化密度矩阵(RDM2)的对角线元素可以作为描述超导态的基本变量，而不是通常在密度泛函方案中被用作基本变量的RDM2的非对角线元素。RDM2的对角线元素被称为成对密度(PD)，它与系统的粒子数波动有直接关系。在本文中，我们认为粒子数的波动可以成为超导态的指示，并且选择PD作为基本变量的密度泛函方案将是有前途的第一性原理理论，用于超导体。 显示英文摘要

摘要： We show that the diagonal elements of the second-order reduced density matrix (RDM2) can be chosen as basic variables for describing the superconducting state, instead of the off-diagonal elements of the RDM2 that are usually adopted as basic variables in the density functional scheme. The diagonal elements of the RDM2 are called pair-density (PD), which is explicitly related to the fluctuation of the particle number of the system. In this paper, we argue that the fluctuation of the particle number can become an indication of the superconducting state, and that the density functional scheme in which the PD is chosen as a basic variable would be a promising first-principles theory for superconductors.