[CPMD-list] Fe calculations

[Eyvaz Isaev]

Dear all,

Now I have my own question. I tried to calculate using
CPMD_3.7 the total energy for a number of lattice
parameters for BCC Iron with one atom in the unit
cell. Input file I have used is attached.
Surprisingly,  I could not start the job on
Athlon/1700 based PC with 512Mb core memory. The same
happened on Athlon/2100 with 1Gb core memory. In both
cases cpmd.x  stops with error about memory
allocation:

****************************************************************
 PROCESSOR     0 ALLOCATION OF   140810176 WORDS OF
MEMORY FAILED

****************************************************************

 PROGRAM STOPS IN SUBROUTINE MEMORY| ALLOCATION FAILED
(SCR)

The job started for small cutoff energy (15Ry), but
there was a restriction for k-mesh, i.e. the  6x6x6
mesh worked, but 8x8x8 mesh did not.  Then I have
observed another puzzle: "grep 'NFI' Fe.out" showed
that the total energy converged, but the last value
was different compared to total energies  for
preceding iterations.

I have to note that CPMD_3.5 works well with
E_cut=60Ry and 20x020x20 k-mesh on the same PC.
Lattice parameter 2.72Ang for BCC Fe, probably, is not
bad for  the LDA calculation. But there is no magnetic
moment though the "LSD" key is mentioned. The above
mentioned difference for the total energy between the
last and preceding
iterations takes place, too (The next cited results
reference to CPMD_3.5).

 ==     NFI=     32      ETOT=    -19.953008   TCPU=  
 397.85 ==
 ==     NFI=     33      ETOT=    -19.953007   TCPU=  
 221.33 ==
 ==     NFI=     34      ETOT=    -19.953006   TCPU=  
 497.17 ==
 ==     NFI=     35      ETOT=    -19.953006   TCPU=  
 236.00 ==
 ==     NFI=     36      ETOT=    -19.953075   TCPU=  
 443.73 ==

 == DRHOMAX= 1.366E-03  DETOT=     2.240E-06    THL=
5.124E-01 ==
 == DRHOMAX= 1.179E-03  DETOT=     6.589E-07    THL=
5.346E-01 ==
 == DRHOMAX= 1.053E-03  DETOT=     1.330E-06   
THL=-1.930E-03 ==
 == DRHOMAX= 1.067E-03  DETOT=    -8.935E-08    THL=
1.861E+00 ==
 == DRHOMAX= 9.999E-04  DETOT=    -6.931E-05    THL=
9.562E-01 ==


I guessed it is due to a rather sharp change of the
parameter DRHOMAX and put 5.D-4 (instead 1.D-3).
It turned out that the suggestion is not true:

 ==     NFI=     20      ETOT=    -19.953006   TCPU=  
 139.03 ==
 ==     NFI=     21      ETOT=    -19.953006   TCPU=  
 120.44 ==
 ==     NFI=     22      ETOT=    -19.953006   TCPU=  
 136.42 ==
 ==     NFI=     23      ETOT=    -19.953006   TCPU=  
  72.60 ==
 ==     NFI=     24      ETOT=    -19.953075   TCPU=  
 218.27 ==

 == DRHOMAX= 6.108E-04  DETOT=    -2.409E-08    THL=
1.091E+00 ==
 == DRHOMAX= 6.504E-04  DETOT=    -6.143E-08    THL=
1.074E+00 ==
 == DRHOMAX= 5.551E-04  DETOT=     1.478E-07   
THL=-1.008E-01 ==
 == DRHOMAX= 5.225E-04  DETOT=     4.693E-08   
THL=-3.112E+00 ==
 == DRHOMAX= 3.774E-04  DETOT=    -6.899E-05    THL=
3.587E-01 ==

One can see that ETOT(24) and ETOT(23) are different
(69 a.u.) again and the convergence  for the last
iteration unexpectedly becomes worser.

Later the problem was fixed using more strong DETOT
(1.D-5). So, this kind of convergence behaviour makes
one be careful everytime about convergence.

Could you please tell me what is wrong in my input
file for total energy calculations and why the job
faild to start for such a small system?
Why Fe is nonmagnetic despite "LSD" key presents?
Besides, may be something is wrong in my notes about
convergence?

Any suggestions are welcome.

Regards,
Eyvaz Isaev, PhD
Senior Scientific Researcher
Theoretical Physics Department
Moscow Steel and Alloys Institute

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Fe_HGH.bat_pade
Type: application/octet-stream
Size: 707 bytes
Desc: Fe_HGH.bat_pade
Url : http://cpmd.org/pipermail/cpmd-list/attachments/20030214/3f10ea36/attachment.obj