The virial theorem and ground state energy estimate of nonlinear Schr\"odinger equations in $\mathbb{R}^2$ with square root and saturable nonlinearities in nonlinear optics

TL;DR

This paper develops a virial theorem and eigenvalue estimates for nonlinear Schrödinger equations with square-root and saturable nonlinearities in two dimensions, providing new tools for analyzing ground state energies in nonlinear optics.

Contribution

It introduces a virial theorem applicable to NLS equations with non-power-law nonlinearities, enabling eigenvalue estimates and ground state energy bounds in R2.

Findings

Derived virial theorem for square-root and saturable nonlinearities.

Established eigenvalue estimates for these NLS equations.

Provided asymptotic lower bounds for ground state energy as nonlinear coefficient grows.

Abstract

The virial theorem is a nice property for the linear Schrodinger equation in atomic and molecular physics as it gives an elegant ratio between the kinetic and potential energies and is useful in assessing the quality of numerically computed eigenvalues. If the governing equation is a nonlinear Schrodinger equation with power-law nonlinearity, then a similar ratio can be obtained but there seems no way of getting any eigenvalue estimate. It is surprising as far as we are concerned that when the nonlinearity is either square-root or saturable nonlinearity (not a power-law), one can develop a virial theorem and eigenvalue estimate of nonlinear Schrodinger (NLS) equations in R2 with square-root and saturable nonlinearity, respectively. Furthermore, we show here that the eigenvalue estimate can be used to obtain the 2nd order term (which is of order $ln\Gamma$) of the lower bound of the ground state energy as the coefficient $\Gamma$ of the nonlinear term tends to infinity.