Review
Molecular models
- intramolecular terms: stretch, bend, torsion
- intermolecular terms: van der Waals, electrostatics, polarization
Electrostatic contributions may be very long-ranged
- monopole-monopole decays as r-1, dipole-dipole as r-3 (in 3D)
Need to consider more than nearest-image interactions
- direct lattice sum not feasible
Ewald sum
- approximate field due to charges by smearing them
- smeared-charge field amenable to Fourier treatment
- correction to smearing needs only nearest-neighbor sum