Structure and Properties of Neat Liquids Using Nonadditive ...

Structure and Properties of Neat Liquids J. Phys. Chem., Vol. 99, No. 16, 1995 6211
Water Neutron Diffraction
C
.- 0
c
0
C
3
U
c
3.0 -
.- 0
c
2 2.0
.-
L c
-
n
II
El
...........
I HHJ
I
0.0
distance (Angstroms)
Figure 1. Water neutron diffraction radial distribution functions from data in ref 18.
Water Po13
4.0
c
.- 0
c
0
t 3
U
c
.- 0
3.0
I
2 2.0
1-
c L
v)
6 -
.- m
'0
2
1 .o
n
r;3 ............
...........
0.0
distance (Angstroms)
Figure 2. Water: POL3 radial distribution functions (T = 300 K, P = 1 bar, 216 moleculesbox, '20 000 step average).
Methanol. The energy components of monomeric and
dimeric methanol for both polarizable and additive models are
presented in Table 5. The dimerization energy is seen to be
-5.6 kcal/mol for the additive model and -5.4 kcaVmol for
the nonadditive model. Earlier work of Jorgensen found an
average dimerization energy of -4.4 kcal/mol for his rigid
The liquid simulations were run for very long trajectories,
the additive simulation was run for 2+ ns (including testing
simulation protocols as well), and the nonadditive was run for
350f ps (the nonadditive model model runs about 4x slower
than the additive). The energetics of the current calculation
are shown in Table 5 and the radial distribution functions (RDFs)
in Figures 6 and 7. The calculated AHvapoization is 8.45 kcaV
mol for the additive model and 9.05 kcal/mol for the nonadditive
model using a scaling factor of 0.88 for the partial charges; the
experimental AHvapofization is -9.0 kcal/mol.20 The densities are
0.775 and 0.820 gm/cm3, respectively, as compared to an
experimental value25 of 0.787 gm/cm3. While the nonadditive
AHvapo"zation is quite good, the system is somewhat too dense.