Unit cell of phase-I ammonia with cubic space-group symmetry and a cell length of 5.185 Å; the labeled N and D atoms constitute the asymmetric unit. The thermal ellipsoids are plotted at the 50 % level using values from a 180 K DFT-MD simulation (see Sec. III A for more details).
Classical 2D probability distribution functions for the D atom in at 180 K plotted in the (a) , (b) , and (c) planes. ( is the longest principal axis; the shortest.)
Classical N–N radial pair distribution functions at (a) 77 K and (b) 180 K. The solid red line represents the results of a simulation for a supercell; the blue dashed line a cell.
Experimental (Ref. 1) and simulated (classical DFT MD) ADPs of the N and D atoms, together with the time-averaged bonded distance and equilibrium correction at 77 and 180 K. The experimental distance correction was derived using the TLS method. The MD correction is given by .
Isotropic displacement parameters of the N and D atoms in determined in classical DFT MD simulations. The results of refinements by Leclercq et al. (Ref. 16) and Hewat and Riekel (Ref. 1) are also shown.
Isotropic displacement parameters of the N and D atoms at 77 K as calculated in classical constant- empirical potential simulations for a variety of supercell sizes.
Isotropic displacement parameters of the N and D atoms for three different unit cell sizes. Values were calculated in classical constant- empirical potential MD simulations of a supercell.
Isotropic displacement parameters of the N and D atoms in from simulations at 77 and 180 K, as determined in classical and PIMD simulations with different numbers of ring-polymer beads (imaginary-time slices), .
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