My Community

If any one can help me to set the parameters for calculating correct Hessian matrix or force constant matrix by vasp.4.6;

Some of my settings are as bellow:
INCAR file
IBRION=5
NSW=1
NFREE=2
POTIM=0.015

KPOINTS file
K-Points
0
Monkhorst Pack
15 15 15
0 0 0

But I have serious problems with the results of Hessian matrix in OUTCAR file:
1) main diagonal elements of matrix are negative;
2) some of its elements are zero but we expected non-zero values;


Thanks in advance for any help.

There should be six elements zero (they coincide with the translation and rotation of the molecule/unit cell). When you calculate the frequencies with VASP, there is always the probability that one or a few of these frequencies are negative, due to numerical accuracy. If the bottom six are close to zero, your result is usually still trustworthy.

please check whether the default value of EDIFF is sufficient to get reliable frequencies, you may need to increase the accuracy substantially (depending on the system you investigate)