Boundary Effects on Eigen-problems of Discrete Laplacian in Lattices

We consider how distribution of eigenvalues depends on boundary conditions of a discrete Laplacian operator on lattices. We study the Laplacian with boundary conditions given by a linear combination of Dirichlet and Neumann con-ditions. In particular, we derive a secular equation and investigate the Laplacian operator’s eigenvalues with different boundary conditions, including the interlacing property, the first eigenvalue gaps, and the monotonicity property.