vasp calculate frequency of iodine

[botaoteng]

Hi, I used vasp to optimize the configuration and calculated the frequency of iodine molecules, and found the frequency of iodine molecule equals 214.5cm-1(which is nearlly the same as experimental results),the box size used is 15*15*15.

Then, I uesd the same method to calculate the frequecy of iodine molecule chains(several iodine molecules array in a line with the distance 3.96 Angstron). BUt the frequency I got is also near 214.5cm-1, which mean that the molecules at two ends does not effect the frequecy of iodine molecules.

I wander, is the energy between molecules much smaller than the bond energy, and the effect of the intermolecular interaction can be neglected, or the iodine molecule is unpolarized, and the intermolecular interaction can not be calculated accurately.

Thank you so much!

INCAR
system=iodine
ISTART=1
ICHARGE=1
IBRION=5
EDIFF=0.0001
EDIFFG=-0.01
NSW=100
POTIM=0.02
NFREE=2
PREC=Accu
ISMEAR=0
SIGMA=0.1



Iodine_2
1.000
15.000 0.000 0.000
0.000 15.000 0.000
0.000 0.000 26.576
8
Selective dynamics
Direct
0.000 0.000 -0.000 T T T
0.000 0.000 0.100 T T T
0.000 0.000 0.250 T T T
0.000 0.000 0.350 T T T
0.000 0.000 0.500 T T T
0.000 0.000 0.600 T T T
0.000 0.000 0.750 T T T
0.000 0.000 0.851 T T T

[support_vasp]

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