c CCLRC
Section 2.3
2.3.1
Short Ranged (van der Waals) Potentials
The short ranged pair forces available in DL POLY 3 are as follows.
1. 12-6 potential: (12-6)
U (r
ij
) =
A
r
12
ij
-
B
r
6
ij
(2.68)
2. Lennard-Jones: (lj)
U (r
ij
) = 4
r
ij
12
-
r
ij
6
(2.69)
U (r
ij
) =
E
o
(n - m)
m
r
o
r
ij
n
- n
r
o
r
ij
m
(2.70)
4. Buckingham potential: (buck)
U (r
ij
) = A exp -
r
ij
-
C
r
6
ij
(2.71)
5. Born-Huggins-Meyer potential: (bhm)
U (r
ij
) = A exp[B( - r
ij
)] -
C
r
6
ij
-
D
r
8
ij
(2.72)
6. Hydrogen-bond (12-10) potential: (hbnd)
U (r
ij
) =
A
r
12
ij
-
B
r
10
ij
(2.73)
7. Shifted force n-m potential [
U (r
ij
) =
E
o
(n - m)
m
n
r
o
r
ij
n
-
1
n
- n
m
r
o
r
ij
m
-
1
m
+
nmE
o
(n - m)
r
ij
- r
o
r
o
n
-
m
,
(2.74)
with
=
(n - m)
[n
m
(1 + (m/ - m - 1)/
m
) - m
n
(1 + (n/ - n - 1)/
n
)]
=
m+1
- 1
n+1
- 1
1
n-m
(2.75)
=
r
cut
r
o
.
This peculiar form has the advantage over the standard shifted n-m potential in that both
E
o
and r
0
(well depth and location of minimum) retain their original values after the shifting
process.
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