Establishing simple relationship between eigenvector and matrix elements

A simple approximate relationship between the ground-state eigenvector and the sum of matrix elements in each row has been established for real symmetric matrices with non-positive off-diagonal elements. Specifically, the i-th components of the ground-state eigenvector could be calculated by a(-S-i)(p) + c, where S-i is the sum of elements in the i-th row of the matrix with p, a and c being variational parameters. The simple relationship provides a straightforward method to directly calculate the ground-state eigenvector for a matrix. Our preliminary applications to the Hubbard model and the Ising model in a transverse field show encouraging results. The simple relationship also provides the optimal initial state for other more accurate methods, such as the Lanczos method. (C) 2020 Elsevier B.V. All rights reserved.