[Pw_forum] Negative frequencies at really low threshold convergence

[Elie M]

Dear all,
I am doing some phonon calculations at the gamma point for a system of 8 atoms . In the scf calculations I used an ultrasoft pseudopotential so I chose my ecutrho= 8* ecutwfc and also in the ph.x calculations tr2_ph was set to 1 *10^(-19) but I still get that the three first values of the frequencies are negative. Does this confirm the instability of the system?
SCF INPUT:
 &system    ibrav=0,    celldm(1)= 9.008277,    nat=8,    ntyp= 2,    ecutwfc =32,    ecutrho=256,    occupations='smearing',    smearing='mv',    degauss=0.02
/ &electrons    conv_thr=1.D-6,    mixing_beta=0.3D0,    mixing_mode='plain',    diago_david_ndim=2,.....etc
PH INPUT:
&inputph
tr2_ph=1.0d-19,prefix='Graphyne',fildvscf='Graphydvscf',recover=.true.,trans=.true.,amass(1)=12.0107,amass(2)=1.00794,outdir='/home_cluster/fis718/eliemouj/espresso-4.3.2/Graphyne/GRAPHYNEDIR/',fildyn='Graphy.dynG'   /0.0 0.0 0.0

The output i got is :
  omega( 1) =     -11.303890 [THz] =    -377.057178 [cm-1]     omega( 2) =     -11.228798 [THz] =    -374.552397 [cm-1]     omega( 3) =      -1.493780 [THz] =     -49.827127 [cm-1]     omega( 4) =       1.499866 [THz] =      50.030148 [cm-1]     omega( 5) =       2.192955 [THz] =      73.149113 [cm-1]     omega( 6) =      11.690342 [THz] =     389.947822 [cm-1].......
Thanks for the help
Elie MouhaesUniversity of NottinghamNG7 2RD



 		 	   		  
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