[Pw_forum] problem with DFT+U

[Paolo Giannozzi]

There are many well-known problems of DFT+U, but none that is known to
crash jobs with an obscure message.

Rank 21 [Thu Jul 16 15:51:04 2015] [c4-2c0s15n2] Fatal error in PMPI_Bcast:
> Message truncated, error stack:
> PMPI_Bcast(1615)..................: MPI_Bcast(buf=0x75265e0, count=160,
> MPI_DOUBLE_PRECISION, root=0, comm=0xc4000000) failed
>

this signals a mismatch between what is sent and what is received in a
broadcast operation. This may be due to an obvious bug, that however should
show up at the first iteration, not after XX. Apart compiler or MPI library
bugs, another reason is the one described in sec.8.3 of the developer
manual: different processes following a different execution paths. From
time to time, cases like this are found  (the latest occurrence, in band
parallelization of exact exchange) and easily fixed. Unfortunately, finding
them (that is: where this happens) typically requires a painstaking
parallel debugging.

Paolo
-- 
Paolo Giannozzi, Dept. Chemistry&Physics&Environment,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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