  In this paper, we present an entropy-stable Gauss collocation discontinuous
Galerkin (DG) method on 3D curvilinear meshes for the GLM-MHD equations: the
single-fluid magneto-hydrodynamics (MHD) equations with a generalized Lagrange
multiplier (GLM) divergence cleaning mechanism. For the continuous entropy
analysis to hold and to ensure Galilean invariance in the divergence cleaning
technique, the GLM-MHD system requires the use of non-conservative terms.
  Traditionally, entropy-stable DG discretizations have used a collocated nodal
variant of the DG method, also known as the discontinuous Galerkin spectral
element method (DGSEM) on Legendre-Gauss-Lobatto (LGL) points. Recently, Chan
et al. ("Efficient Entropy Stable Gauss Collocation Methods". SIAM -2019)
presented an entropy-stable DGSEM scheme that uses Legendre-Gauss points
(instead of LGL points) for conservation laws. Our main contribution is to
extend the discretization technique of Chan et al. to the non-conservative
GLM-MHD system.
  We provide a numerical verification of the entropy behavior and convergence
properties of our novel scheme on 3D curvilinear meshes. Moreover, we test the
robustness and accuracy of our scheme with a magneto-hydrodynamic
Kelvin-Helmholtz instability problem. The numerical experiments suggest that
the entropy-stable DGSEM on Gauss points for the GLM-MHD system is more
accurate than the LGL counterpart.
