Abstract
D
2 (160) molecules distributed over a (16
×
16) patch of LiF(0
0
1) surface, where the (+) sign represents the cationic
Li
+ site, and (−) sign represents the anionic
F
−
site.
Classical Monte Carlo (MC) simulations of D
2 molecules physisorbed on LiF(0
0
1) surfaces are reported and show a series of interesting commensurate structure forms, viz.,
p(2
×
2) →
p(8
×
2) →
p(4
×
2), with coverages
Θ
=
0.5, 0.625, and 0.75, respectively, and are stable up to 8
K. These structures are consistent with recent helium atom scattering (HAS) results (the
p(4
×
2) is not observed) in terms of coverage and stability, but disagree in terms of symmetry. The
p(2
×
2) structure contains two D
2 molecules per unit cell, with each molecule lying parallel to the plane of the surface directly above every other cationic site. For the
p(4
×
2) structure, there are two kinds of adsorption sites: a parallel site, as in the case of
p(2
×
2), and a tilted site, where the D
2 molecules sit between cationic and anionic sites with the molecular axis directed toward the anionic site, with a tilt angle of
θ
∼
63°. Perturbation theory calculations show that the adsorbed D
2 molecules are azimuthally delocalized and hence the structures are indeed
c-type. Our calculations also indicate that
o-D
2 and helicoptering
p-D
2 species prefer cationic sites, compared to cartwheeling
p-D
2 species.