The ABINIT Users Mailing List ( CLOSED )

[Pio Baettig <baettigp@gmx.net>]

Dear abinit users,

I have found a small inconsistency when doing geometry optimizations of 
a rhombohedral (R3c) system.
The angles and vectors stay the same (as given by the space group) for 
about ten geometry iterations, and then one starts to diverge slightly.
Within the limits of the space group, they should be the same.
I guess, this is a problem of the floating-point precision?
Below the worst case, I encountered so far, the first angle deviates by 
0.5 mdegrees from the two others.


 Angles (23,13,12)=  5.96739156E+01  5.96739156E+01  5.96739156E+01 degrees
  angles (23,13,12)=  59.67391564  59.67391564  59.67391564 degrees
  angles (23,13,12)=  59.65429950  59.65429950  59.65429950 degrees
  angles (23,13,12)=  59.60987717  59.60987717  59.60987717 degrees
  angles (23,13,12)=  59.59774016  59.59774016  59.59774016 degrees
  angles (23,13,12)=  59.58954710  59.58954710  59.58954710 degrees
  angles (23,13,12)=  59.58994126  59.58994126  59.58994126 degrees
  angles (23,13,12)=  59.59640191  59.59640191  59.59640191 degrees
  angles (23,13,12)=  59.60556657  59.60556657  59.60556657 degrees
  angles (23,13,12)=  59.61517982  59.61517982  59.61517982 degrees
  angles (23,13,12)=  59.62547486  59.62547486  59.62547486 degrees
  angles (23,13,12)=  59.64340038  59.64340037  59.64340037 degrees ! 
start of divergence
  angles (23,13,12)=  59.66163347  59.66163344  59.66163344 degrees
  angles (23,13,12)=  59.67145659  59.67145646  59.67145646 degrees
  angles (23,13,12)=  59.67329734  59.67329688  59.67329688 degrees
  angles (23,13,12)=  59.67356472  59.67356266  59.67356266 degrees
  angles (23,13,12)=  59.67416017  59.67414948  59.67414948 degrees
  angles (23,13,12)=  59.67575367  59.67570578  59.67570578 degrees
  angles (23,13,12)=  59.67768192  59.67750735  59.67750735 degrees
  angles (23,13,12)=  59.67851421  59.67798716  59.67798716 degrees
                           ^            ^            ^

     acell    1.0086679784E+01  1.0086679784E+01  1.0086679784E+01 Bohr
  acell=  1.0086679784E+01  1.0086679784E+01  1.0086679784E+01
  acell=  1.0095845448E+01  1.0095845448E+01  1.0095845448E+01
  acell=  1.0107077039E+01  1.0107077039E+01  1.0107077039E+01
  acell=  1.0105341284E+01  1.0105341284E+01  1.0105341284E+01
  acell=  1.0100122543E+01  1.0100122543E+01  1.0100122543E+01
  acell=  1.0097132505E+01  1.0097132505E+01  1.0097132505E+01
  acell=  1.0093418047E+01  1.0093418047E+01  1.0093418047E+01
  acell=  1.0092339678E+01  1.0092339678E+01  1.0092339678E+01
  acell=  1.0092419651E+01  1.0092419651E+01  1.0092419651E+01
  acell=  1.0092238158E+01  1.0092238159E+01  1.0092238159E+01 ! start 
of divergence
  acell=  1.0090904084E+01  1.0090904084E+01  1.0090904084E+01
  acell=  1.0088374760E+01  1.0088374763E+01  1.0088374763E+01
  acell=  1.0086037737E+01  1.0086037745E+01  1.0086037745E+01
  acell=  1.0084928271E+01  1.0084928299E+01  1.0084928299E+01
  acell=  1.0084184900E+01  1.0084185025E+01  1.0084185025E+01
  acell=  1.0083734213E+01  1.0083734862E+01  1.0083734862E+01
  acell=  1.0084085342E+01  1.0084088246E+01  1.0084088246E+01
  acell=  1.0084919226E+01  1.0084929815E+01  1.0084929815E+01
  acell=  1.0085332361E+01  1.0085364332E+01  1.0085364332E+01
     acell    1.0085332361E+01  1.0085364332E+01  1.0085364332E+01 Bohr
                     ^                 ^                 ^



The optimized atomic positions remain in the initially determined space 
group, so if three equal angles and acell are given for a subsequent 
scf, R3c is the space group obtained.
(The same behaviour is also observed for optcell 3)

BAO.in
------
kptopt 1
ngkpt 6 6 6
ecut 45.0
pawecutdg  60

optcell 2
ionmov 2
dilatmx 1.05
ecutsm 0.5
ntime 25

getwfk 1

acell 10.086679784 10.086679784 10.086679784 bohr
angdeg  59.67391564  59.67391564  59.67391564
ntypat 3
znucl 83 13 8
natom 10
typat 1 1 2 2 3 3 3 3 3 3
xred
0.00000000000000    0.00000000000000    0.00000000000000
0.50000000000320    0.50000000000320    0.50000000000320
0.27141788893320    0.27141788893320    0.27141788893320
0.77141788893320    0.77141788893320    0.77141788893320
0.54462841053320    0.98371566192320    0.07314091094120
0.07314091094120    0.54462841053320    0.98371566192320
0.98371566192320    0.07314091094120    0.54462841053320
0.48371566192320    0.04462841053420    0.57314091094320
0.04462841053420    0.57314091094320    0.48371566192320
0.57314091094320    0.48371566192320    0.04462841053420

nstep 100
toldfe 1.0d-10
diemac 12.0
nsppol 1
-----

Which set of angles and vectors should be taken for subsequent scf-runs?

Thank you very much for any hints.

Best regards,

Pio Baettig