Using ph.x to calculate phonon frequencies.

A typical QE workflow relies on three distinct components:

| Error message | Likely cause | Fix | |---|---|---| | Error in routine diagonalization (1) | Insufficient memory | Reduce nbnd , lower ecutwfc | | SCF convergence not achieved | Bad starting guess or mixing | Increase mixing_beta , try diagonalization = 'cg' | | ibrav not set correctly | Wrong lattice type | Check QE ibrav table (0 = free cell) | | No pseudopotential found | Wrong path | Set pseudo_dir correctly |

&CONTROL calculation = 'scf' ! Self-consistent field calculation restart_mode = 'from_scratch', pseudo_dir = './pseudo/', ! Directory for pseudopotentials outdir = './tmp/', ! Directory for temporary large files prefix = 'silicon', / &SYSTEM ibrav = 2, ! Bravais lattice index (2 for FCC) celldm(1) = 10.26, ! Lattice constant in Bohr nat = 2, ! Number of atoms ntyp = 1, ! Number of atom types ecutwfc = 30.0, ! Kinetic energy cutoff for wavefunctions (Ry) / &ELECTRONS conv_thr = 1.0d-8, ! Convergence threshold /

A standard course curriculum follows this logical progression of exercises.