[Pw_forum] PWscf and highly parallel machines

[Nicola Marzari]

Paolo Umari has also implemented a conjugate gradients minimization
in CP.

so, for a CP calculation, in which the only thing you need is the
electronic ground state of a given structure, this would be the best
strategy - our few tests were that it was 3-4 times more effective than
damped dynamics. If you want to relax a structure, you should do, after
this first electronic calculation, a combined damped dynamics on 
electrons and ions.

One thing we haven't tested is the relative performance of PWSCF and
CP - my guess is that the algorithms of PWSCF are much faster, although
the balance might change as the system becomes larger and larger.
In principle, the CP algorithm is variational, so should always 
converge, but again this is rarely a problem.

Bottom line - advantages for PWSCF is that it should be faster for most
systems of interest. CP uses much less memory, and should be very 
efficient in calculating H|psi>, so the balance when going towards very
large scale or very parallel calculations would be extremely interesting
to explore.

Any comparative test, under controlled conditions, would be very useful.

				nicola


Paolo Giannozzi wrote:
> 
> On Feb 14, 2007, at 18:48 , Nichols A. Romero wrote:
> 
>> If one were to use CP across such a large number of processors,
>> what algorithm is your best bet for minimizing your electronic d.o.f.,
>> sd or cg
> 
> steepest descent is very inefficient and should be used only
> for the initial steps of a simulation or in desperate cases. The
> "standard" way of minimizing electronic degrees of freedom
> in CP is damped dynamics
> 
> Paolo
> ---
> Paolo Giannozzi, Democritos and University of Udine, Italy
> 
> 
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Prof Nicola Marzari   Department of Materials Science and Engineering
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