Hello, my question is in the context of modeling static neutron stars via the TOV equation. This is for a 20 week research project for my undergraduate degree. I am creating different equations of state to relate energy density to pressure, I have already used ideal fermi gas models, and now wish to add (very) basic nuclear interactions via an attractive yukawa potential and a repulsive 1/r^n model (modeling Pauli exclusion principle). I have no formal education in GR, but since I need to use the TOV equation for the modeling I have picked up what I could. I also have no formal education in nuclear physics. Currently as I understand it, all energies cause gravity. But now I am trying to understand what a negative potential energy means. For example, if we assume positrons and electrons have the exact same rest mass in a flat space time at infinity, and we consider a small charge neutral test mass, sufficiently far away, does a positron-positron system exert a greater gravitational "force" on the test mass than an electron-positron system because of the difference in coulomb potential energy? A follow up question would be if there are differences, does a region of negative energy density repel objects?