Hello all:<br>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 <br>
<br>%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br> from scale_h : error # 1<br> Not enough space allocated for radial FFT: try restarting with a larger cell_factor.<br> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%<br>
<br>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<br><br>------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<br>
Total force = 0.000027 Total SCF correction = 0.000004<br> SCF correction compared to forces is too large, reduce conv_thr<br><br><br> entering subroutine stress ...<br><br> total stress (Ry/bohr**3) (kbar) P=-3539.67<br>
-0.02405899 0.00000000 0.00000000 -3539.20 0.00 0.00<br> 0.00000000 -0.02405899 0.00000000 0.00 -3539.20 0.00<br> 0.00000000 0.00000000 -0.02406857 0.00 0.00 -3540.61<br>
<br><br> BFGS Geometry Optimization<br><br> number of scf cycles = 1<br> number of bfgs steps = 0<br><br> enthalpy new = -573.6572611922 Ry<br><br> new trust radius = 0.2000000000 bohr<br>
new conv_thr = 1.0E-10 Ry<br><br> new unit-cell volume = 1258.11889 a.u.^3 ( 186.43398 Ang^3 )<br><br>CELL_PARAMETERS (alat)<br> 0.963490012 0.000000000 0.000000000<br> -0.481745006 0.834406827 0.000000000<br>
0.000000000 0.000000000 1.854979314<br>-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<br>
<br>the bfge calculation go on in 3 step and stop with the above error. the input file:<br><br>-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<br>
&CONTROL<br> calculation = 'vc-relax' ,<br> restart_mode = 'from_scratch' ,<br> wf_collect = .true. ,<br> outdir = '/lustre/AIOFM/gxgu/workLCAF/temp/' ,<br>
wfcdir = '/lustre/AIOFM/gxgu/workLCAF/wftemp/' ,<br> pseudo_dir = '/home/AIOFM/gxgu/work/NCPP/' ,<br> prefix = 'LCAF' ,<br> etot_conv_thr = 1.0D-7 ,<br>
forc_conv_thr = 1.0D-6 ,<br> nstep = 100 ,<br> tstress = .true. ,<br> tprnfor = .true. ,<br> dipfield = .true. ,<br> /<br> &SYSTEM<br>
ibrav = 4,<br> celldm(1) = 9.4490,<br> celldm(3) = 1.9253,<br> nat = 18,<br> ntyp = 4,<br> ecutwfc = 30 ,<br>
ecutrho = 120 ,<br> nosym = .true. ,<br> /<br> &ELECTRONS<br> electron_maxstep = 100,<br> conv_thr = 1.0D-10 ,<br> /<br>&IONs<br> ion_dynamics = 'bfgs' ,<br>
/<br>&CELL<br> cell_dynamics = 'bfgs' ,<br>/<br>ATOMIC_SPECIES<br> Li 6.94100 03-Li.LDA.fhi.UPF <br> Al 26.98154 13-Al.LDA.fhi.UPF <br> Ca 40.07800 20-Ca.LDA.fhi.UPF <br> F 18.99840 09-F.LDA.fhi.UPF <br>
ATOMIC_POSITIONS crystal <br> Li 0.333333333 0.666666667 0.250000000 <br> Li 0.666666667 0.333333333 0.750000000 <br> F 0.375595671 0.008455746 0.142528376 <br> F 0.991544254 0.367139925 0.142528376 <br>
F 0.632860075 0.624404329 0.142528376 <br> F 0.991544254 0.624404329 0.357471624 <br> F 0.632860075 0.008455746 0.357471624 <br> F 0.375595671 0.367139925 0.357471624 <br>
F 0.624404329 0.991544254 0.857471624 <br> F 0.008455746 0.632860075 0.857471624 <br> F 0.367139925 0.375595671 0.857471624 <br> F 0.008455746 0.375595671 0.642528376 <br>
F 0.367139925 0.991544254 0.642528376 <br> F 0.624404329 0.632860075 0.642528376 <br> Al 0.666666667 0.333333333 0.250000000 <br> Al 0.333333333 0.666666667 0.750000000 <br>
Ca 0.000000000 0.000000000 0.000000000 <br> Ca 0.000000000 0.000000000 0.500000000 <br>K_POINTS automatic <br> 16 16 16 0 0 0 <br>-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------<br>
<br>Do you have some advises for the solution the case or elimination the Raman negative frequencies, any help is greatly appreciated. <br><br>Thanks in advance <br> Wang Di<br>