The high-pressure phase transition in the deuterated lithium hydroxide crystalline state has been studied by Car-Parrinello molecular dynamics simulations, in the constant pressure, constant-temperature ensemble. The recently developed metadynamics approach has been applied to encourage the system to transform into different phases in an affordable simulation time. A previously not completely characterized high-pressure phase has been obtained. The structural and spectroscopic properties have been studied and compared with the neutron scattering, infrared and Ramon measurements. It has been found that the calculated structure differs slightly from the experimental hypothesis, and that the presence of strong hydrogen bonds is the source of the red shift and of the characteristic features of the OD-stretching bands in both IR and Roman spectra.