Eigenvalues did not converge during minimization

[mesonepigreco]

Sometimes, during the minimization, the eigenvalues do not converge, causing an error that halts the code.

This seems to happen especially with the new line-minimization feature, and in systems with big unit cells (>100 atoms)

[mesonepigreco]

It happens in the new gold thermal expansion example sometimes.

[mesonepigreco]

It should not come from the self.update() as this error is now handled there, maybe in the preconditioning of the structure?

[ManexAlkorta]

What is the output of SSCHA when this occurs? I’m having problems with a system of around 200 atoms. Without a root representation it founds imaginary modes at some point in the minimisation, while with the root represantation the the Free energy is fluctuating at some point

[mesonepigreco]

Hi, this is not the issue of the imaginary frequencies, in this case (which is very hard to reproduce) the code halts with an internal error that the numpy library is not able to diagonalize the dynamical matrix (the error state that the eigenvalue problem is not converging).

In your case, you can probably start with the root representation and then switch it off after some steps with something like:

minim.root_representation = "sqrt"
minim.max_ka = 100 # Set the maximum number of steps
minim.run()
minim.max_ka = 1000 # Maximum number of steps
minim.root_representation = "normal"
minim.run()

You can adapt the script to your use