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fix_momentum.cpp
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Created
Thu, Aug 22, 06:29
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3 KB
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text/x-c
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Sat, Aug 24, 06:29 (2 d)
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blob
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20080418
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rLAMMPS lammps
fix_momentum.cpp
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/* ----------------------------------------------------------------------
LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
http://lammps.sandia.gov, Sandia National Laboratories
Steve Plimpton, sjplimp@sandia.gov
Copyright (2003) Sandia Corporation. Under the terms of Contract
DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
certain rights in this software. This software is distributed under
the GNU General Public License.
See the README file in the top-level LAMMPS directory.
------------------------------------------------------------------------- */
#include "stdlib.h"
#include "string.h"
#include "fix_momentum.h"
#include "atom.h"
#include "domain.h"
#include "group.h"
#include "error.h"
#include "force.h"
using
namespace
LAMMPS_NS
;
using
namespace
FixConst
;
/* ----------------------------------------------------------------------
Contributing author: Naveen Michaud-Agrawal (Johns Hopkins U)
------------------------------------------------------------------------- */
/* ---------------------------------------------------------------------- */
FixMomentum
::
FixMomentum
(
LAMMPS
*
lmp
,
int
narg
,
char
**
arg
)
:
Fix
(
lmp
,
narg
,
arg
)
{
if
(
narg
<
4
)
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
nevery
=
force
->
inumeric
(
FLERR
,
arg
[
3
]);
if
(
nevery
<=
0
)
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
linear
=
angular
=
0
;
int
iarg
=
4
;
while
(
iarg
<
narg
)
{
if
(
strcmp
(
arg
[
iarg
],
"linear"
)
==
0
)
{
if
(
iarg
+
4
>
narg
)
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
linear
=
1
;
xflag
=
force
->
inumeric
(
FLERR
,
arg
[
iarg
+
1
]);
yflag
=
force
->
inumeric
(
FLERR
,
arg
[
iarg
+
2
]);
zflag
=
force
->
inumeric
(
FLERR
,
arg
[
iarg
+
3
]);
iarg
+=
4
;
}
else
if
(
strcmp
(
arg
[
iarg
],
"angular"
)
==
0
)
{
angular
=
1
;
iarg
+=
1
;
}
else
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
}
if
(
linear
==
0
&&
angular
==
0
)
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
if
(
linear
)
if
(
xflag
<
0
||
xflag
>
1
||
yflag
<
0
||
yflag
>
1
||
zflag
<
0
||
zflag
>
1
)
error
->
all
(
FLERR
,
"Illegal fix momentum command"
);
// cannot have 0 atoms in group
if
(
group
->
count
(
igroup
)
==
0
)
error
->
all
(
FLERR
,
"Fix momentum group has no atoms"
);
}
/* ---------------------------------------------------------------------- */
int
FixMomentum
::
setmask
()
{
int
mask
=
0
;
mask
|=
END_OF_STEP
;
return
mask
;
}
/* ---------------------------------------------------------------------- */
void
FixMomentum
::
init
()
{
masstotal
=
group
->
mass
(
igroup
);
}
/* ---------------------------------------------------------------------- */
void
FixMomentum
::
end_of_step
()
{
if
(
linear
)
{
double
vcm
[
3
];
group
->
vcm
(
igroup
,
masstotal
,
vcm
);
// adjust velocities by vcm to zero linear momentum
// only adjust a component if flag is set
double
**
v
=
atom
->
v
;
int
*
mask
=
atom
->
mask
;
int
nlocal
=
atom
->
nlocal
;
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
if
(
mask
[
i
]
&
groupbit
)
{
if
(
xflag
)
v
[
i
][
0
]
-=
vcm
[
0
];
if
(
yflag
)
v
[
i
][
1
]
-=
vcm
[
1
];
if
(
zflag
)
v
[
i
][
2
]
-=
vcm
[
2
];
}
}
if
(
angular
)
{
double
xcm
[
3
],
angmom
[
3
],
inertia
[
3
][
3
],
omega
[
3
];
group
->
xcm
(
igroup
,
masstotal
,
xcm
);
group
->
angmom
(
igroup
,
xcm
,
angmom
);
group
->
inertia
(
igroup
,
xcm
,
inertia
);
group
->
omega
(
angmom
,
inertia
,
omega
);
// adjust velocities to zero omega
// vnew_i = v_i - w x r_i
// must use unwrapped coords to compute r_i correctly
double
**
x
=
atom
->
x
;
double
**
v
=
atom
->
v
;
int
*
mask
=
atom
->
mask
;
imageint
*
image
=
atom
->
image
;
int
nlocal
=
atom
->
nlocal
;
double
dx
,
dy
,
dz
;
double
unwrap
[
3
];
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
if
(
mask
[
i
]
&
groupbit
)
{
domain
->
unmap
(
x
[
i
],
image
[
i
],
unwrap
);
dx
=
unwrap
[
0
]
-
xcm
[
0
];
dy
=
unwrap
[
1
]
-
xcm
[
1
];
dz
=
unwrap
[
2
]
-
xcm
[
2
];
v
[
i
][
0
]
-=
omega
[
1
]
*
dz
-
omega
[
2
]
*
dy
;
v
[
i
][
1
]
-=
omega
[
2
]
*
dx
-
omega
[
0
]
*
dz
;
v
[
i
][
2
]
-=
omega
[
0
]
*
dy
-
omega
[
1
]
*
dx
;
}
}
}
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