The V-OH and V-OD centers in MgO, CaO, and SrO have been investigated at th
e ab initio quantum-mechanical level, by using the CRYSTAL98 periodic progr
am, the Hartree-Fock Hamiltonian, the supercell scheme, and a localized bas
is set. The defects, formally obtained by substituting a hydrogen atom for
a cation, exhibit a large relaxation of H from the perfect lattice position
towards one of the oxygens, and the formation of a strong O-H covalent bon
d, as documented by the calculated bond populations and O-H vibrational fre
quencies, which are in good agreement with infrared frequencies. The unpair
ed electron is fully localized on the oxygen opposite to H with respect to
the M (M = Mg, Ca, Sr) vacancy. The first evaluations of the Fermi contact,
the anisotropic component of the hyperfine coupling tensor, and the electr
ic-field gradient at the H atom are reported and compared successfully with
electron paramagnetic resonance and electron-nuclear double resonance expe
rimental data. The defect is also characterized in terms of charge- and spi
n-density maps, band structures, defect formation, and relaxation energies.
The stability of the results as a function of the supercell size is docume
nted.