Dear users

I have attached the output of phonon calculation for Al pure bulk. I used symmetry and optimized the bulk Al with taking its primitive cell. All frequencies in phononDisp are positive except q-pt 26 and 27 (I have attached it). All frequencies in phononDOS file are positive except q-pt 51 and 56. What is the problem?

I have attched optimization output file (Al_opt.castep).

By the way, in the phononDOS.castep file, the code has used supercell, but I used primitive for all calculation!!!

Thank you for your helps.