[Pw_forum] Fortran runtime error

[Paolo Giannozzi]

On Sep 13, 2009, at 14:04 , Ihsan Erikat wrote:

> Fortran runtime error: ALLOCATE: Out of memory

>      G cutoff = 5499.5703  (2391129 G-vectors)     FFT grid: (150,  
> 75,432)

if you want to perform calculations on large systems, you need
to have an idea of how much time and memory you need. From
the above data, you can easily calculate
2391129*3*8/1024/1024 = 55Mb just for the list of G vectors;
150*75*432*8/1024/1024= 39Mb for each real, 2*39Mb for
each complex array on the FFT grid (charge, potential, etc).
These are not even the largest arrays.

As a rule of thimb, if you increase the size of the unit cell by
a factor N, the required memory increases as N^2

P.
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Paolo Giannozzi, Dept of Physics, University of Udine
via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222