[gmx-users] normal mode analysis - regd

[ramesh cheerla]

Dear  Gromacs users,

              I am performing normal mode analysis (NMA) for a crystal, but
in the vibrational spectrum that obtained from NMA,  there are no low
frequency lattice modes ( i.e., no peaks in spectrum below 50 cm-1).  But
the spectrum that have obtained from velocity auto correlation function
(VACF) contains these low frequency peaks.
Here my doubt is why NMA was unable to capture  these low frequency
peaks(modes) ?

Can anybody please help me in this regard.

Thank you in advance.



Best,
Ramesh