S. Tsuneyuki et al., Quantum-mechanical properties of protons in solid molecular hydrogen at megabar pressures, J L TEMP PH, 122(3-4), 2001, pp. 291-296
Quantum distributions of protons in three high-pressure phases of solid mol
ecular hydrogen are investigated by the first-principles path integral mole
cular dynamics (FP-PIMD) method, in which interatomic forces are calculated
precisely based on the density functional theory. The distributions have e
ntirely different symmetries from those predicted by conventional simulatio
n with classical treatment of protons. Especially in phase II, we found tha
t molecular rotation is hindered by quantum fluctuation of protons, having
a strong resemblance to a quantum distribution of impurity muonium in cryst
alline silicon. The mechanism of this "quantum localization" is clarified b
y a detailed study of the potential energy surface for the molecular rotati
on.