[Pw_forum] dE0s is positive which should never happen

[Guntram Schmidt]

Dear All,

I tried to optimize a crystal structure of a molecular compound and get 
this strange error. Is there something I've forgotten in the input file?
I've chosen a small ecutwfc to make some "preoptimization" - is it okay 
to do so (I'm still not able to converge the cutoffs - see my other post)?

&control
    calculation = 'relax'
    restart_mode='from_scratch',
    prefix='i2t0480',
    tstress = .true.
    tprnfor = .true.
    pseudo_dir = '/gpfs/home/aasfu/espresso-4.3.1/pseudo/',
    outdir='/gpfs/home/aasfu/tmp/'
    verbosity = 'high'
/
&system
  ibrav = 14,
  A = 8.2555,
  B = 17.0986,
  C = 16.3082,
  cosAB = 0,
  cosAC = -.4968073528,
  cosBC = 0,
  nat = 196,
  ntyp = 5,
  occupations = 'fixed',
  ecutwfc = 20,
  ecutrho = 80,
  input_dft = 'vdW-DF'
/
&electrons
     conv_thr        = 1.0d-5
     electron_maxstep= 1000
/
&ions
/

ATOMIC_SPECIES
  P 39.974 P.rpb-nc.UPF
  O 15.999 O.rpb-nc.UPF
  N 14.007 N.rpb-nc.UPF
  C 12.011 C.rpb-nc.UPF
  H 1.0079 H.rpb-nc.UPF


ATOMIC_POSITIONS angstrom
  H      -4.163902    3.036540    7.286078 1 1 1
  C      -3.730208    5.027159    7.959787 1 1 1
  H      -2.669409    4.951703    7.725352 1 1 1
  C      -4.231111    6.183196    8.511764 1 1 1
  H      -3.568842    7.024960    8.708593 1 1 1
and 210 more atoms...



The output says after 41 cycles of geometry optimizations in the 
subroutine stress:



    0:     number of scf cycles    =  30
    0:     number of bfgs steps    =  28
    0:
    0:     energy   old            =   -1592.2501932245 Ry
    0:     energy   new            =   -1547.5620256423 Ry
    0:
    0:     CASE: energy  _new > energy  _old
    0:
    0:
    0: 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    0:     from bfgs : error #         1
    0:     dE0s is positive which should never happen
    0: 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
    0:
    0:     stopping ...

The strange thing is, that the energy was not -1592... before at all:
grep '!' i2t0480.xyz.relax.20.rpb-nc.UPF.out
    0:!    total energy              =   -1542.41391161 Ry
    0:!    total energy              =   -1544.87249615 Ry
    0:!    total energy              =   -1546.30689086 Ry
    0:!    total energy              =   -1546.89859418 Ry
    0:!    total energy              =   -1547.07908001 Ry
    0:!    total energy              =   -1547.12438175 Ry
    0:!    total energy              =   -1547.16304879 Ry
    0:!    total energy              =   -1547.21850898 Ry
    0:!    total energy              =   -1547.26799568 Ry
    0:!    total energy              =   -1547.31147437 Ry
    0:!    total energy              =   -1547.33202922 Ry
    0:!    total energy              =   -1547.35963149 Ry
    0:!    total energy              =   -1547.36650754 Ry
    0:!    total energy              =   -1547.38045447 Ry
    0:!    total energy              =   -1547.38597654 Ry
    0:!    total energy              =   -1547.39351928 Ry
    0:!    total energy              =   -1547.40184806 Ry
    0:!    total energy              =   -1547.41383843 Ry
    0:!    total energy              =   -1547.43030750 Ry
    0:!    total energy              =   -1547.45110560 Ry
    0:!    total energy              =   -1547.47294386 Ry
    0:!    total energy              =   -1547.48424959 Ry
    0:!    total energy              =   -1547.48774725 Ry
    0:!    total energy              =   -1547.49458349 Ry
    0:!    total energy              =   -1547.50098365 Ry
    0:!    total energy              =   -1547.50487139 Ry
    0:!    total energy              =   -1547.50802242 Ry
    0:!    total energy              =   -1547.51133404 Ry
    0:!    total energy              =   -1547.51564694 Ry
    0:!    total energy              =   -1547.52054790 Ry
    0:!    total energy              =   -1547.52614229 Ry
    0:!    total energy              =   -1547.53597920 Ry
    0:!    total energy              =   -1547.54614655 Ry
    0:!    total energy              =   -1547.55021920 Ry
    0:!    total energy              =   -1547.55191818 Ry
    0:!    total energy              =   -1547.55360256 Ry
    0:!    total energy              =   -1547.55527582 Ry
    0:!    total energy              =   -1547.55697509 Ry
    0:!    total energy              =   -1547.55871207 Ry
    0:!    total energy              =   -1547.56042619 Ry
    0:!    total energy              =   -1547.56202564 Ry


Thanks a lot for help,
Guntram