CASTEP

# Frequently Asked Questions

## Licencing

- Am I eligible for an academic license and if so what must I do?
- If I am not eligible for an academic license, how can I obtain CASTEP?

## Getting Help

- Where can I get help running CASTEP?
- I posted to the CASTEP email list asking for help but nobody answered. What can I do to get an answer?

## Getting started

## SCF convergence

## Geometry Optimization

- How can I check whether my geometry optimization really converged?
- My BFGS geometry optimization did not converge. What can I do?
- Which geometry optimization method should I use?
- Should I trust the "Estimated frequency and bulk modulus" printed by a geometry optimisation?

## Bandstructure and DOS

- How can I quickly generate a density-of-states plot?
- How can I plot partial densities of states?
- How can I generate an electronic density of states with the sharp features I expect?
- How can I generate a bandstructure plot?
- How can I generate a publication quality electronic band structure with the bands properly joined up?
- Why does my OPTADOS density of states plot not look like the one using dos.pl, even for fixed Gaussian smearing?
- My bandstructure looks a mess with many very short segments.
- How can I checkpoint and restart a bandstructure calculation?

## Phonon and related calculations

- How can I calculate phonons for a spin-polarized system?
- How can I do a phonon calculation with DFT+D?
- My Raman calculation gives huge numbers or nonsense or "*" characters for the intensity. Why?
- How can I perform a "mode-following"calculation explore the energy of a function of amplitude for a particular phonon mode?
- I performed a phonon DOS calculation. Do I need to repeat all that calculation if I want dispersion curves as well?
- How can I generate a phonon DOS with both sharp and curved features as in textbook examples? I just get a wiggly mess from dos.pl.
- How can I compute a phonon projected density of states?

## Magnetic resonance calculations

- For what kind of molecules and crystals can CASTEP provide reliable NMR predictions?
- I completed a NMR ab initio simulation, now how can I compare it with my experimental spectra?
- How can I checkpoint and restart a MAGRES calculation?

## Pseudopotentials

- Which pseudopotential library should I use for functionality which only works with norm-conserving pseudopotentials?
- What pseudopotential libraries are available for use with CASTEP?

## Postprocessing and Visualisation

- How can I create an animation of a geometry optimisation or MD trajectory from my calculation??
- How can I create an animation of phonon modes from my calculation??
- How can I visualise the results of an NMR chemical shift calculation?
- How can I visualise electron density or spin density??

## Run-time failure messages

- My run aborted with a message of the type "Error XXXX: Failed to open YYYY file"
*wave_orthonormalise_overlap_wv_ks: ztrtri failed in inversion**Error writing wavefunction coefficients to file in wave_write_all_par**Error reading wavefunction coefficients from file in wave_read_all_par*

## Interfacing with other codes

## General problems getting a run to work

- How should I choose the best number of cores for a parallel run on Archer?
- My job stopped before it reached the end. How can I find out how and why it failed?
- My HECToR/Archer job fails and the the messages in the PBS log file talk about the "OOM Killer". What does this mean?
- How many atoms can I sensibly include in my model?
- How can I check my input files do not have a mistake before submitting to the batch queue?
- How can I find out how much memory my run will use?