R. Ramirez et al., LOW-ENERGY QUANTUM DYNAMICS OF ATOMS AT DEFECTS - INTERSTITIAL OXYGENIN SILICON, Journal of physics. Condensed matter, 9(15), 1997, pp. 3107-3116
The problem of the low-energy highly anharmonic quantum dynamics of is
olated impurities in solids is addressed by using path-integral Monte
Carlo simulations. Interstitial oxygen in silicon is studied as a prot
otypical example showing such a behaviour. The assignment of a 'geomet
ry' to the defect is discussed. Depending on the potential (or on the
impurity mass), there is a 'classical' regime, where the maximum proba
bility density for the oxygen nucleus is at the potential minimum. The
re is another regime, associated with highly anharmonic potentials, wh
ere this is not the case. The two regimes are separated by a sharp tra
nsition. Also, the decoupling of the many-nuclei problem into a one-bo
dy Hamiltonian to describe the low-energy dynamics is studied. The adi
abatic potential obtained from the relaxation of all of the other degr
ees of freedom at each value of the coordinate associated with the low
-energy motion gives the best approximation to the full many-nuclei pr
oblem.