Si diamond known-geometry control (exp a=5.4309 A, Fd-3m primitive)

Known-geometry control for the DFT relax route (ABACUS). Si diamond primitive cell at experimental a=5.4309 A. Reference: PBE relaxes to a_conv=5.469 A (+0.7%, MP mp-149 GGA). Route settings matched to the MnAlGe contract run: PBE, DZP, ecutwfc 65, kspacing 0.16, scf_thr 1e-6, mp smearing 0.05 eV, broyden 0.4, no U.