Electrostatic interactions enter DFTB/xTB Hamiltonian as charge dependent energy expression. Allows evaluation of electronic energy, which is calculated from core Hamiltonian, H0 (see #2) and charge-dependent Hamiltonian, H1.
Workflow:
solve eigenvalue problem with Hamiltonian
obtain density matrix
calculate populations / partial charges
evaluate (charge-dependent) energy expression
obtain potential / field, i.e. derivative of energy expression w.r.t. populations / partial charges (sign convention!)
Electrostatic interactions enter DFTB/xTB Hamiltonian as charge dependent energy expression. Allows evaluation of electronic energy, which is calculated from core Hamiltonian, H0 (see #2) and charge-dependent Hamiltonian, H1.
Workflow:
Fortran reference implementation:
Note: