Dear all,,

I'm trying to comput the Raman spectrum of a first stage potassium graphite intercalation compound using CASTEP. I built a cell (attached) and optimized it using GGA WC functional with the "Fine" quality presets. My settings are also attached. Everything is fine and the lattice parameters are in agreement with literature. My next step is to compute the Raman spectrum. So I take the optimized structure and start Energy calculation with same parameters but this time selecting the "Polarizability, IR and Raman spectra" in Properties tab. First thing which happens, CASTEP tells me that my structure (which was optimized already) needs to be optimized before the property can be computed. Ok, I select "Yes", the job starts and after a period of time gives me an error. When I look into Efield.castep file I see the warning "Warning: electronic minimisation did not converge when finding ground state." followed by several errors: "Error check_elec_ground_state : electronic_minimisation of initial cell failed. Current trace stack: check_elec_ground_state  castep". What am I doing wrong?

Thanks!