Hey guys, I am trying to extract the hessian matrix from the fchk file to check its invertibility, however I am confused because my molecule has 22 atoms and is nonlinear, hence 3*22-6=60 vibrational degrees of freedom, thusthe hessian should have 60*60=3600 entries, but the total number of entries in that cartesian force constant is 2211, which is more than 1770 the number of entries in the upper triangle of the hessian matrix, or 1830, where the diagonal is involved
So what are those cartesian force constant exactly since they are slightly more than half to be the entries of the hessian …