How to calculate the energy of one liquid water or the self-energy of an isolated water molecule in lammps?

Dear lammps users,

I tried to calculate the hydration energy of a surface. In order to do that, I need to calculate the the energy of one liquid water molecule,which is the sum of the calculated self-energy of an isolated water molecule and the condensation energy of water.

I tried to get the self-energy of an isolated water molecule through energy minimization in lammps, but the value(-0.0061606862 Kcal/mol) seemed not correct.

Please help.

Best wishe,

Kane