Comment Re:...wow... (Score 1) 171
Actually, in classical molecuar dynamics, the algorithm is usually N^2. However, in this case "N" is the number of _electrons_, not atoms, i.e. 42000 electrons.
Oh, and this is not classical physics, but QM. Thus each electrons wave function has to be represented by a (possibly substantial) set of basis functions. Not sure if anyone's been able to get Density Functional Theory (DFT) to scale that high, but if so, DFT scales as (IIRC) either N^7 or N^9. Ouch! Sure there are tricks, such as pseudopotentials that "lump" the inner electron-shells with the nucleus, but still it'd be quite a big deal, and require quite some big iron.
FWIW, I ran some very simple DFT calculations with only ONE atom that took roughly 1-second on a single Power5 processor. Unfortunately for me, I needed to do several million of them -- hence why I ran on a 500 processor machine a block away from BlueGene/L.
Oh, and this is not classical physics, but QM. Thus each electrons wave function has to be represented by a (possibly substantial) set of basis functions. Not sure if anyone's been able to get Density Functional Theory (DFT) to scale that high, but if so, DFT scales as (IIRC) either N^7 or N^9. Ouch! Sure there are tricks, such as pseudopotentials that "lump" the inner electron-shells with the nucleus, but still it'd be quite a big deal, and require quite some big iron.
FWIW, I ran some very simple DFT calculations with only ONE atom that took roughly 1-second on a single Power5 processor. Unfortunately for me, I needed to do several million of them -- hence why I ran on a 500 processor machine a block away from BlueGene/L.
