Dear Prof. Julian,

I have been trying to get eigenvectors from Atomic Simulation Enviornment (ASE) which matches exactly with the eigenvectors coming from GULP(lattice dynamics software,FORTRAN).

GULP produces eigenvectors(it uses LAPACK pacakge).I need to get the same eigenvectors but with ASE(it does not have scipy at its backend,and so no LAPACK).

**I am using the same k-points in GULP as well as ASE softwares)**

But when I include **scipy.eigh** for solving the eigenvectors in ASE, the eigenvectors do not match with the GULPâ€™s eigenvectors (although the dynamical matrix is matching for both).

**Question:**

(1)ASE uses â€śfinite-displacement method where the derivatives of the total energy and effective potential are obtained from finite-difference approximationsâ€ť. Does GULP also uses the same technique?

(a)If **yes**,then could you tell me the:

```
(i) Series of **source files** name used to reach the eigenvector and eigenvalues (where LAPACK and EISPACK libraries are called in order to calculate eigenvalue and eigenvectors)?
(ii) The *finite displacement value* to be input (eg. *delta = 0.05 Angs* in ASE)
```

(b) If **no**, then the approach used?

(FORTRAN is new to me and so was difficult to traceback inside GULP software as to which LAPACK function is being called).

Could you please help me out.

Thanks in advance.