Anisotropic potentials

Changes to the input dataset:

To input the anisotropic short range parameters

BUCK NI CODA CL CODA
10549.321 0.264206 28.490 0.0 70.0
ANIS NI CODA CL CODA
0 0 1 0 1 -0.022080
0 0 0 1 1 0.026758
0 0 2 0 2 0.004878
0 0 0 2 2 -0.101149
ENDS

ANIS should follow immediately after the parameters for the BUCK part.
The lines after ANIS are
k1 k2 l1 l2 j rho
RHO(0) is read in in the above example as the first parameter of the BUCK potential; this value is EXP(ALPHA * RHO(0)).
You can read it in as rho(0) by supplying a line after anis
0 0 0 0 0 rho(o), in which case you will get a warning message.
The second parameter after BUCK is 1.0/ALPHA, the third is the Van der Waals parameter.
To convert from anisotropic to isotropic, just remove ANIS and the lines following it.

On the output file, the first parameter of the BUCK potential is reset to zero and the correct value of rho(0) is printed out even if it was not input.
At present to input a potential between two species that are the same you need to supply both of the identical interactions.

BUCK CL CODA CL CODA
15555.674 0.271759 57.363 0.0 70.0
ANIS CL CODA CL CODA
0 0 0 1 1 0.026758
0 0 1 0 1 0.026758
0 0 0 2 2 -0.101149
0 0 2 0 2 -0.101149
ENDS

Note: This can be set up automatically using NEIGHBOURS.

Input of the axis system for the anisotropic atoms
This must be put in after the molecular axes (MOLX) but before the following ENDS

ANIS
..
..
CLR1 CODA
Z LINE CAR1 CODA CLR1 CODA 1
X PLANE CAR1 CODA NIT1 CODA 1 NIT3 CODA 1
..
..
NIT1 CODA
Z BIEX NIT1 CODA CAR1 CODA 1 CAR2 CODA 1
X PLANE NIT1 CODA CAR1 CODA 1 CAR2 CODA 1
..
..
ENDS

Format:
Record 1 Species on which the anisotropic axis is to lie

Record 2 First axis, format
[X,Y,Z] [LINE,BIEX,BIIN] species1 species 2 separation(1-2) [species 3 separation(1-3)]
LINE is as for molecular axes; the species in line do not have to contain the species on which you are constructing the axis.
BIEX BIIN are external and internal bisector of a bond angle. The species are in the order centre of bond end 1 separation 1 end 2 separation 2 so the bond angle is 2-1-3.

Record 3 Second axis which must be a plane, same format as for MOLX
The sequence is terminated by an ENDS record; note that this will give you two ENDS records in a row.
The calculated anisotropic axes are printed out.

Note: This needs to be set up by modifying the dmain file manually.