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The
energy of the angle formed by the atoms i,
j and k, Ea-ijk
is:
Ea-ijk
= Ka-ijk[
Aijk -
Ao-ijk
]2
where
A is the angle formed by the ordered atoms
i, j and k,
Ka is the force constant and
A0 is the equilibrium
angle.
The
Angle record must appear only after the
Atom Inclusion Types have been defined. This
record must also appear after the Atom Inclusion
Group record if Groups are used in this
record. The Angle record has the following
format:
|
:ANGLE
|
|
|
:Typei:Typej:Typek:
|
Ka-ijk
|
A0-ijk
|
|
|
:Typei:Typej:Typek:
|
Ka-ijk
|
A0-ijk
|
|
|
...
|
...
|
...
|
|
:END
|
The
opening and closing keywords, like all keywords,
begin with a colon and start on column one of their
respective lines. The body of the data section may
contain any number of lines. A line may be empty or
may contain a list of three Atom Inclusion
Type or Group names followed by two
numbers. The names are written amongst four colons;
the colons are not part of the names. The first
number is the force constant in units of
kcal/mol/radian2. The second number is
the equilibrium bond angle in degree. Following the
second number may be text to serve as comment. The
comment must be separated, by white space, from the
second number.
An
angle type defined for Inclusion Atom Types
:A:B:C: will serve equally well for an angle of
Types :C:B:A:. Only the first instance of a
definition of an angle type will be saved.
Subsequent definitions for the same angle type will
be silently ignored. Therefore, definitions using
Groups should be placed at the end of the
list so that the generic definitions do not
override the specific definitions.
The
program Yup.fpf
will expand Groups into their component
Types, hash each trio of Types into a
numerical code, and sort the codes. This forms the
index table. The force constants are converted to
internal units used by
YUP
and with the equilibrium angle these numbers form
the data table. The index and data tables are
written to the unformatted file:
"Angle
Constants".
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