Vibrational Frequency Calculation: Imaginary Frequencies from Optimized Minimum structures (H2O)
Posted: Mon Jan 30, 2023 7:06 pm
Hi,
I need to get the vibrational frequency calculation for the Metal doped Graphene. After the calculations, there are four imaginary frequencies, and some imaginary frequencies are higher (1.028868 cm-1, 1.334421 cm-1, 3.595799 cm-1, 125.990998 cm-1).
Then I wanted to run for H2O molecule as a test frequency calculation. The results are the same as the Metal doped Graphene. I could run the vibrational frequency calculation for H2O molecule after the relax calculation. But there are three imaginary frequencies for this H2O molecule. I don’t understand why is showing the imaginary frequencies for the optimized minimum structure.
Could you please explain me and figure out and what should I do for the frequency calculation.
I have attached my files of H2O.
Thank you.
INCAR:
System = FREQ
ISTART = 0
ICHARG = 2
PREC=Accurate
EDIFF=1E-6
ENMAX = 450
ISMEAR = 0
SIGMA = 0.05
LREAL=Auto
IBRION = 5
ISIF = 2
NSW = 1
EDIFFG = -0.01
ALGO=Fast
NFREE = 2
POTIM=0.005
KPOINTS:
KPoints-point
0
Monkhorst Pack
3 3 1
0 0 0
POSCAR
H2O _2
1.0000000000000000
8.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 8.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 8.0000000000000000
O H
1 2
Direct
-0.0000340711360937 0.0000000000000000 0.0000000000000000
0.0745271855680487 0.9040070284914102 0.0000000000000000
0.0745271855680487 0.0959929715085898 0.0000000000000000
Imaginary frequencies of first frequency calculation (H2O):
5.875007 cm-1, 148.058529 cm-1, 202.491147 cm-1
Then I increased EDIFF to 1E-8. After that the imaginary frequency (H2O) are;
3.087036 cm-1, 53.908671 cm-1, 77.342731 cm-1
I need to get the vibrational frequency calculation for the Metal doped Graphene. After the calculations, there are four imaginary frequencies, and some imaginary frequencies are higher (1.028868 cm-1, 1.334421 cm-1, 3.595799 cm-1, 125.990998 cm-1).
Then I wanted to run for H2O molecule as a test frequency calculation. The results are the same as the Metal doped Graphene. I could run the vibrational frequency calculation for H2O molecule after the relax calculation. But there are three imaginary frequencies for this H2O molecule. I don’t understand why is showing the imaginary frequencies for the optimized minimum structure.
Could you please explain me and figure out and what should I do for the frequency calculation.
I have attached my files of H2O.
Thank you.
INCAR:
System = FREQ
ISTART = 0
ICHARG = 2
PREC=Accurate
EDIFF=1E-6
ENMAX = 450
ISMEAR = 0
SIGMA = 0.05
LREAL=Auto
IBRION = 5
ISIF = 2
NSW = 1
EDIFFG = -0.01
ALGO=Fast
NFREE = 2
POTIM=0.005
KPOINTS:
KPoints-point
0
Monkhorst Pack
3 3 1
0 0 0
POSCAR
H2O _2
1.0000000000000000
8.0000000000000000 0.0000000000000000 0.0000000000000000
0.0000000000000000 8.0000000000000000 0.0000000000000000
0.0000000000000000 0.0000000000000000 8.0000000000000000
O H
1 2
Direct
-0.0000340711360937 0.0000000000000000 0.0000000000000000
0.0745271855680487 0.9040070284914102 0.0000000000000000
0.0745271855680487 0.0959929715085898 0.0000000000000000
Imaginary frequencies of first frequency calculation (H2O):
5.875007 cm-1, 148.058529 cm-1, 202.491147 cm-1
Then I increased EDIFF to 1E-8. After that the imaginary frequency (H2O) are;
3.087036 cm-1, 53.908671 cm-1, 77.342731 cm-1