# [QE-users] Negative Frequency in Phonon calculation

LEUNG Clarence liangxy123 at hotmail.com
Sat Jan 12 10:08:30 CET 2019

```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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