[DFTB-Plus-User] On parallel version of DFTB+

[ZHAOHUI HUANG]

Can you describe some algorithm details used in DFTB+？ especially on Hamiltonian diagonalization? Tight-binding calculations are supposed to run very fast, but your reply impressed me with totally different picture. It takes me time to think over your words. I have not realized that DFTB+ might require a few thousand of processors. simply ask, could you tell me on what most CPU time are spent with DFTB+ calculation? diagonalization?
thanks a lot. 

If you use iterative method to solve Hamiltonian eigenvalues as implemented in BerkeleyGW, what do you think the calculation speed?

ZhaoHui Huang,


----- Original Message -----
From: "Jacek Jakowski" <jjakowski at gmail.com>
To: "User list for DFTB+ related questions" <dftb-plus-user at mailman.zfn.uni-bremen.de>
Sent: Saturday, September 17, 2016 8:26:15 PM
Subject: Re: [DFTB-Plus-User] On parallel version of DFTB+

Most likely you don't have enough memory to fit the 26,000 atoms  on
your computer, even if   DFTB+ can handle it.   Assuming that  your
26k atoms are carbons (or similar) you need 80GB   to fit a single
matrix (100kbasis) in memory and much more (like 10 times)  for a real
calculations.
But then  if this fits into  your memory, then  100k matrices on 4000
cores takes about 10 hours for a  single diagonalization (real case).
It would  probably  took  something like a month  to do SCF, and
about half  a year for  a few  MD steps.

I suggest  that you decrease  the size of cell so that your matrices
are below  32,000.

Jacek

On Fri, Sep 9, 2016 at 1:36 PM, ZHAOHUI HUANG <zuh101 at psu.edu> wrote:
> Hello,
>
>      Sorry to bother you if not interested.
>
>      I have an issue from running parallel DFTB+. My unit cell contains 26,000 atoms and I just want to relax the structures a few steps. By running the code, I first get output overflow error message, then I increase MAXRECL parameter defined in HSDParser package. It runs indeed. but It failed by SCALAPACK error,
>
> MAXNEIGHBORS: 8847
>   iSCC Total electronic   Diff electronic      SCC error
> Operation failed!
> ppotrf in scalafx_ppotrf_dreal
> Info: 23233
>
>
>     Is there any code developer who is familiar with this part of code? thanks.
>
>
> ZhaoHui Huang,
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