plane wave and band: why(how) are they different?


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Gets Around
I have a question to Mr. Bylaska. I've been trying to wrap my mind around it: why are plane wave code and band codes (sort of) different in NWChem, e.g. they implemented as different modules? I can;t quite understand that. All the codes (CRYSTAL, VASP etc.) regardless whether they use basis set or waves, always sample grid of k points in reciprocal space. I assume band in NWchem does the same, but what's the purpose of plane wave code alone then? In other words, what's the catch here, aren't they simply the same thing only plane wave (PSPW) uses one k point, whereas band (NWPW) uses the specified grid? Could Eric elaborate or give some references? What would be similarities and differences, especially in applications?

thanks