Selective interactions

By default, DL_FIELD will look for all possible two-body (bond), three-body (angle), and four-body (dihedral) interactions, based on the bond connections. However, DL_FIELD allows a selection of these interactions to be excluded and will not be considered in the DL_POLY simulation runs.

These optional directives are always defined after the CONNECT statements in MOLECULE templates.

../../_images/Orange_bar6.png

REMOVE, ONLY and OFF directives

These directives must always be used in conjunction with the body interaction directives: BOND, ANGLE and DIHEDRAL. They are used to selectively include or exclude certain types of interactions. Diagram below illustrates the use of these directives.

../../_images/dlf_18_1.png

Note that each directive takes several parameters depending on types of interactions. For example:

BOND REMOVE label_1 label_2

ANGLE ONLY label_1 label_2 label_3

Example below shows the use of selective interaction directives in a calcium carbonate MOLECULE template:

MOLECULE calcium_carbonate1  5  0.0
Ca1 Ca2+#3_ternary_oxide1     1.668                  OAR1
C1  C4+#3_ternary_oxide1      0.999                   |      aragonite, calcite
O1  O2-#2_ternary_oxide1     -0.889            Ca    CAR1
O1  O2-#2_ternary_oxide1     -0.889                 /   \
O1  O2-#2_ternary_oxide1     -0.889               OAR1  OAR1
CONNECT  Ca1 > 0 AUTO
CONNECT  C1  > 3 AUTO
CONNECT  O1  > 1 AUTO
CONNECT  O1  > 1 AUTO
CONNECT  O1  > 1 AUTO
ANGLE ONLY O1 C1 O1
IMPROPER C1 O1 O1 O1
END MOLECULE

To completely remove a type of interaction, use the OFF directive. For example:

DIHEDRAL OFF

Will remove all dihedral terms.

Warning

Avoid conflicting statements such as ANGLE OFF and ANGLE ONLY directives appeared within a same MOLECULE template.


../../_images/Orange_bar6.png

Remove 1-4 non-bonded interactions

An atom pair that is separated by three bonds will usually be treated with vdw and coulombic interactions, called the 1-4 non-bonded interactions, and often scaled with some scaling factors. Such interaction can be switched off selectively within a MOLECULE. The syntax is as follows:

EXCLUSION_14 label_1 label_2 …

Each of such statement includes a group of ATOM_LABELs and exclusions will apply if any 1-4 atom pairs are identified within the atom group. Up to a number of 15 ATOMs can be specified in a statement.

Note

More than one EXCLUSION_14 statements can be defined within a MOLECULE and they are independant from each other. The 1-4 exclusions only apply to the respective group of atoms defined in each statement.


^ GO TO TOP ^