[Pw_forum] vc-relax problem when calculate lattice parameters

[Wang Di]

Hello all:
i wish to calculate the Raman spectra of the crystal with espresso 4.1.1
package. However, the  calculated frequencies included negative value.
According to the pwscf manual, the unstable structure or the bad scf
calculation cause the negative value, I know the structure of the material
is stable below the melt point, so I perform the relax of the atom position,
and change difference PP (GGA, LDA) to test. Unlucky, the changes still
exist the negative frequencies and the calculated frequencies different from
the experimental value totally.  recently, according to some references
about the Raman spectra calculation with espresso, the optimization of
lattice parameters is needed, I performing vc-relax calculation, but the job
stop with the error that

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
     from scale_h : error #         1
     Not enough space allocated for radial FFT: try restarting with a larger
cell_factor.
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

according previous questions in mail list, the error means the G value
change too much. From the out file, the first step scf calculation, the
total force was so small

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Total force =     0.000027     Total SCF correction =     0.000004
     SCF correction compared to forces is too large, reduce conv_thr


     entering subroutine stress ...

          total   stress  (Ry/bohr**3)                   (kbar)
P=-3539.67
  -0.02405899   0.00000000   0.00000000      -3539.20      0.00      0.00
   0.00000000  -0.02405899   0.00000000          0.00  -3539.20      0.00
   0.00000000   0.00000000  -0.02406857          0.00      0.00  -3540.61


     BFGS Geometry Optimization

     number of scf cycles    =   1
     number of bfgs steps    =   0

     enthalpy new            =    -573.6572611922 Ry

     new trust radius        =       0.2000000000 bohr
     new conv_thr            =            1.0E-10 Ry

     new unit-cell volume =   1258.11889 a.u.^3 (   186.43398 Ang^3 )

CELL_PARAMETERS (alat)
   0.963490012   0.000000000   0.000000000
  -0.481745006   0.834406827   0.000000000
   0.000000000   0.000000000   1.854979314
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

the bfge calculation go on in 3 step and stop with the above error.  the
input file:

-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
 &CONTROL
                 calculation = 'vc-relax' ,
                restart_mode = 'from_scratch' ,
                  wf_collect = .true. ,
                      outdir = '/lustre/AIOFM/gxgu/workLCAF/temp/' ,
                      wfcdir = '/lustre/AIOFM/gxgu/workLCAF/wftemp/' ,
                  pseudo_dir = '/home/AIOFM/gxgu/work/NCPP/' ,
                      prefix = 'LCAF' ,
               etot_conv_thr = 1.0D-7 ,
               forc_conv_thr = 1.0D-6 ,
                       nstep = 100 ,
                     tstress = .true. ,
                     tprnfor = .true. ,
                    dipfield = .true. ,
 /
 &SYSTEM
                       ibrav = 4,
                   celldm(1) = 9.4490,
                   celldm(3) = 1.9253,
                         nat = 18,
                        ntyp = 4,
                     ecutwfc = 30 ,
                     ecutrho = 120 ,
                       nosym = .true. ,
 /
 &ELECTRONS
            electron_maxstep = 100,
                    conv_thr = 1.0D-10 ,
 /
&IONs
                ion_dynamics = 'bfgs' ,
/
&CELL
               cell_dynamics = 'bfgs' ,
/
ATOMIC_SPECIES
   Li    6.94100  03-Li.LDA.fhi.UPF
   Al   26.98154  13-Al.LDA.fhi.UPF
   Ca   40.07800  20-Ca.LDA.fhi.UPF
    F   18.99840  09-F.LDA.fhi.UPF
ATOMIC_POSITIONS crystal
   Li      0.333333333    0.666666667    0.250000000
   Li      0.666666667    0.333333333    0.750000000
    F      0.375595671    0.008455746    0.142528376
    F      0.991544254    0.367139925    0.142528376
    F      0.632860075    0.624404329    0.142528376
    F      0.991544254    0.624404329    0.357471624
    F      0.632860075    0.008455746    0.357471624
    F      0.375595671    0.367139925    0.357471624
    F      0.624404329    0.991544254    0.857471624
    F      0.008455746    0.632860075    0.857471624
    F      0.367139925    0.375595671    0.857471624
    F      0.008455746    0.375595671    0.642528376
    F      0.367139925    0.991544254    0.642528376
    F      0.624404329    0.632860075    0.642528376
   Al      0.666666667    0.333333333    0.250000000
   Al      0.333333333    0.666666667    0.750000000
   Ca      0.000000000    0.000000000    0.000000000
   Ca      0.000000000    0.000000000    0.500000000
K_POINTS automatic
  16 16 16   0 0 0
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Do you have some advises for the solution the case or elimination the Raman
negative frequencies, any help is greatly appreciated.

Thanks in advance
 Wang Di
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