Quantum criticality at the infinite complete basis set limit: A thermodynamic analog of the Yang and Lee theorem

Finite size scaling for calculations of the critical parameters of the few-body Schrödinger equation is based on taking the number of elements in a complete basis set as the size of the system. We show in an analogy with Yang and Lee theorem, which states that singularities of the free energy at phase transitions occur only in the thermodynamic limit, that singularities in the ground state energy occur only in the infinite complete basis set limit. To illustrate this analogy in the complex-parameter space, we present calculations for Yukawa type potential, and a Coulomb type potential for two-electron atoms.