[QE-users] Negative Frequency in Phonon calculation

[LEUNG Clarence]

Dear QE users,

I use Ph.x to calculate the ZPE and frequency of adsorbed N2 molecules on surface, except the gas the surface is fixed. But the results show that some negative frequency in fixed atom, why?

The result and input file is shown below:

     Mode symmetry, C_1 (1)     point group:

     freq (  1 -  1) =      -1221.6  [cm-1]   --> A               I+R
     freq (  2 -  2) =       -972.9  [cm-1]   --> A               I+R
     freq (  3 -  3) =       -772.4  [cm-1]   --> A               I+R
     freq (  4 -  4) =       -636.6  [cm-1]   --> A               I+R
     freq (  5 -  5) =       -466.0  [cm-1]   --> A               I+R
     freq (  6 -  6) =       -266.5  [cm-1]   --> A               I+R
     freq (  7 -  7) =       -167.5  [cm-1]   --> A               I+R
     freq (  8 -  8) =        -93.4  [cm-1]   --> A               I+R
     freq (  9 -  9) =        -54.9  [cm-1]   --> A               I+R
     freq ( 10 - 10) =        -49.0  [cm-1]   --> A               I+R
     freq ( 11 - 11) =        -32.7  [cm-1]   --> A               I+R
     freq ( 12 - 12) =        -25.1  [cm-1]   --> A               I+R
     freq (196 -196) =         95.3  [cm-1]   --> A               I+R
     freq (197 -197) =        453.7  [cm-1]   --> A               I+R
     freq (198 -198) =        504.5  [cm-1]   --> A               I+R
     freq (199 -199) =        605.5  [cm-1]   --> A               I+R
     freq (200 -200) =        712.9  [cm-1]   --> A               I+R
     freq (201 -201) =       1080.1  [cm-1]   --> A               I+R
     freq (202 -202) =       1179.6  [cm-1]   --> A               I+R
     freq (203 -203) =       1219.7  [cm-1]   --> A               I+R
     freq (204 -204) =       1261.5  [cm-1]   --> A               I+R
     freq (205 -205) =       1563.9  [cm-1]   --> A               I+R
     freq (206 -206) =       3291.5  [cm-1]   --> A               I+R
     freq (207 -207) =       3398.0  [cm-1]   --> A               I+R


&INPUTPH
  prefix='n2',
  tr2_ph = 1d-12,
  ldisp = .true. ,
  epsil=.false.,
  trans=.true.,
  nq1 = 1 ,
  nq2 = 1 ,
  nq3 = 1 ,
  nat_todo = 2,
  alpha_mix(1) = 0.07,
  recover = .true. ,
/
66 67

Many thanks

CLarence
CIty University of Hong Kong
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