How to input Hessian

[7cube]

I want to use Gaussian to calculate hessian matrix for the first step, and I notice geomeTRIC can read hessian.txt from disk. But what should I do to change the hessian from “Gaussian format” to “Numpy format”? Do I only need to convert the triangular matrix got from Gaussian to a symmetric matrix? Should I change the units?

[leeping]

You only need to convert it to a square matrix format. I am 99% sure that the Hessian output from Gaussian is in atomic units (Hartree/bohr^2), and that is also what geomeTRIC uses.

[7cube]

Thank you！

[leehiufung911]

Thank you！

Hello, did you eventually figure out how to do this? I'm trying to do the same thing, trying to get the hessian from a gaussian freq calculation
I can't actually find the triangular matrix in gaussian's output either

[leeping]

I currently don't have a Gaussian frequency calculation handy to provide a detailed response. However, if a Gaussian frequency calculation does not print the Hessian (aka force constant matrix) in the output, then it will be in the .chk file which you can convert to a human-readable format with formchk. Then it is just a matter of extracting the matrix into a separate file.