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fix_spring.cpp
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Tue, Aug 6, 12:13
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rLAMMPS lammps
fix_spring.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.
------------------------------------------------------------------------- */
/* ----------------------------------------------------------------------
Contributing author: Paul Crozier (SNL)
------------------------------------------------------------------------- */
#include "math.h"
#include "stdlib.h"
#include "string.h"
#include "fix_spring.h"
#include "atom.h"
#include "update.h"
#include "respa.h"
#include "domain.h"
#include "error.h"
#include "group.h"
using
namespace
LAMMPS_NS
;
#define TETHER 0
#define COUPLE 1
/* ---------------------------------------------------------------------- */
FixSpring
::
FixSpring
(
LAMMPS
*
lmp
,
int
narg
,
char
**
arg
)
:
Fix
(
lmp
,
narg
,
arg
)
{
if
(
narg
<
9
)
error
->
all
(
"Illegal fix spring command"
);
vector_flag
=
1
;
size_vector
=
3
;
scalar_vector_freq
=
1
;
extensive
=
1
;
if
(
strcmp
(
arg
[
3
],
"tether"
)
==
0
)
{
if
(
narg
!=
9
)
error
->
all
(
"Illegal fix spring command"
);
styleflag
=
TETHER
;
k_spring
=
atof
(
arg
[
4
]);
xflag
=
yflag
=
zflag
=
1
;
if
(
strcmp
(
arg
[
5
],
"NULL"
)
==
0
)
xflag
=
0
;
else
xc
=
atof
(
arg
[
5
]);
if
(
strcmp
(
arg
[
6
],
"NULL"
)
==
0
)
yflag
=
0
;
else
yc
=
atof
(
arg
[
6
]);
if
(
strcmp
(
arg
[
7
],
"NULL"
)
==
0
)
zflag
=
0
;
else
zc
=
atof
(
arg
[
7
]);
r0
=
atof
(
arg
[
8
]);
if
(
r0
<
0
)
error
->
all
(
"R0 < 0 for fix spring command"
);
}
else
if
(
strcmp
(
arg
[
3
],
"couple"
)
==
0
)
{
if
(
narg
!=
10
)
error
->
all
(
"Illegal fix spring command"
);
styleflag
=
COUPLE
;
igroup2
=
group
->
find
(
arg
[
4
]);
if
(
igroup2
==
-
1
)
error
->
all
(
"Could not find fix spring couple group ID"
);
group2bit
=
group
->
bitmask
[
igroup2
];
k_spring
=
atof
(
arg
[
5
]);
xflag
=
yflag
=
zflag
=
1
;
if
(
strcmp
(
arg
[
6
],
"NULL"
)
==
0
)
xflag
=
0
;
else
xc
=
atof
(
arg
[
6
]);
if
(
strcmp
(
arg
[
7
],
"NULL"
)
==
0
)
yflag
=
0
;
else
yc
=
atof
(
arg
[
7
]);
if
(
strcmp
(
arg
[
8
],
"NULL"
)
==
0
)
zflag
=
0
;
else
zc
=
atof
(
arg
[
8
]);
r0
=
atof
(
arg
[
9
]);
if
(
r0
<
0
)
error
->
all
(
"R0 < 0 for fix spring command"
);
}
else
error
->
all
(
"Illegal fix spring command"
);
}
/* ---------------------------------------------------------------------- */
int
FixSpring
::
setmask
()
{
int
mask
=
0
;
mask
|=
POST_FORCE
;
mask
|=
POST_FORCE_RESPA
;
return
mask
;
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
init
()
{
masstotal
=
group
->
mass
(
igroup
);
if
(
styleflag
==
COUPLE
)
masstotal2
=
group
->
mass
(
igroup2
);
if
(
strcmp
(
update
->
integrate_style
,
"respa"
)
==
0
)
nlevels_respa
=
((
Respa
*
)
update
->
integrate
)
->
nlevels
;
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
setup
()
{
if
(
strcmp
(
update
->
integrate_style
,
"verlet"
)
==
0
)
post_force
(
1
);
else
{
((
Respa
*
)
update
->
integrate
)
->
copy_flevel_f
(
nlevels_respa
-
1
);
post_force_respa
(
1
,
nlevels_respa
-
1
,
0
);
((
Respa
*
)
update
->
integrate
)
->
copy_f_flevel
(
nlevels_respa
-
1
);
}
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
post_force
(
int
vflag
)
{
if
(
styleflag
==
TETHER
)
spring_tether
();
else
spring_couple
();
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
spring_tether
()
{
double
xcm
[
3
];
group
->
xcm
(
igroup
,
masstotal
,
xcm
);
// fx,fy,fz = components of k * (r-r0)
double
dx
,
dy
,
dz
,
fx
,
fy
,
fz
,
r
,
dr
;
dx
=
xcm
[
0
]
-
xc
;
dy
=
xcm
[
1
]
-
yc
;
dz
=
xcm
[
2
]
-
zc
;
if
(
!
xflag
)
dx
=
0.0
;
if
(
!
yflag
)
dy
=
0.0
;
if
(
!
zflag
)
dz
=
0.0
;
r
=
sqrt
(
dx
*
dx
+
dy
*
dy
+
dz
*
dz
);
dr
=
r
-
r0
;
fx
=
k_spring
*
dx
*
dr
/
r
;
fy
=
k_spring
*
dy
*
dr
/
r
;
fz
=
k_spring
*
dz
*
dr
/
r
;
// apply restoring force to atoms in group
// f = -k*(r-r0)*mass/masstotal
double
**
f
=
atom
->
f
;
int
*
mask
=
atom
->
mask
;
int
*
type
=
atom
->
type
;
double
*
mass
=
atom
->
mass
;
int
nlocal
=
atom
->
nlocal
;
ftotal
[
0
]
=
ftotal
[
1
]
=
ftotal
[
2
]
=
0.0
;
force_flag
=
0
;
double
massfrac
;
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
if
(
mask
[
i
]
&
groupbit
)
{
massfrac
=
mass
[
type
[
i
]]
/
masstotal
;
fx
*=
massfrac
;
fy
*=
massfrac
;
fz
*=
massfrac
;
f
[
i
][
0
]
-=
fx
;
f
[
i
][
1
]
-=
fy
;
f
[
i
][
2
]
-=
fz
;
ftotal
[
0
]
-=
fx
;
ftotal
[
1
]
-=
fy
;
ftotal
[
2
]
-=
fz
;
}
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
spring_couple
()
{
double
xcm
[
3
],
xcm2
[
3
];
group
->
xcm
(
igroup
,
masstotal
,
xcm
);
group
->
xcm
(
igroup2
,
masstotal2
,
xcm2
);
// fx,fy,fz = components of k * (r-r0)
double
dx
,
dy
,
dz
,
fx
,
fy
,
fz
,
r
,
dr
;
dx
=
xcm2
[
0
]
-
xcm
[
0
]
-
xc
;
dy
=
xcm2
[
1
]
-
xcm
[
1
]
-
yc
;
dz
=
xcm2
[
2
]
-
xcm
[
2
]
-
zc
;
if
(
!
xflag
)
dx
=
0.0
;
if
(
!
yflag
)
dy
=
0.0
;
if
(
!
zflag
)
dz
=
0.0
;
r
=
sqrt
(
dx
*
dx
+
dy
*
dy
+
dz
*
dz
);
dr
=
r
-
r0
;
fx
=
k_spring
*
dx
*
dr
/
r
;
fy
=
k_spring
*
dy
*
dr
/
r
;
fz
=
k_spring
*
dz
*
dr
/
r
;
// apply restoring force to atoms in group
// f = -k*(r-r0)*mass/masstotal
double
**
f
=
atom
->
f
;
int
*
mask
=
atom
->
mask
;
int
*
type
=
atom
->
type
;
double
*
mass
=
atom
->
mass
;
int
nlocal
=
atom
->
nlocal
;
ftotal
[
0
]
=
ftotal
[
1
]
=
ftotal
[
2
]
=
0.0
;
force_flag
=
0
;
double
massfrac
;
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
{
if
(
mask
[
i
]
&
groupbit
)
{
massfrac
=
mass
[
type
[
i
]]
/
masstotal
;
f
[
i
][
0
]
+=
fx
*
massfrac
;
f
[
i
][
1
]
+=
fy
*
massfrac
;
f
[
i
][
2
]
+=
fz
*
massfrac
;
ftotal
[
0
]
+=
fx
*
massfrac
;
ftotal
[
1
]
+=
fy
*
massfrac
;
ftotal
[
2
]
+=
fz
*
massfrac
;
}
if
(
mask
[
i
]
&
group2bit
)
{
massfrac
=
mass
[
type
[
i
]]
/
masstotal2
;
f
[
i
][
0
]
-=
fx
*
massfrac
;
f
[
i
][
1
]
-=
fy
*
massfrac
;
f
[
i
][
2
]
-=
fz
*
massfrac
;
}
}
}
/* ---------------------------------------------------------------------- */
void
FixSpring
::
post_force_respa
(
int
vflag
,
int
ilevel
,
int
iloop
)
{
if
(
ilevel
==
nlevels_respa
-
1
)
post_force
(
vflag
);
}
/* ----------------------------------------------------------------------
return components of total spring force on fix group
------------------------------------------------------------------------- */
double
FixSpring
::
compute_vector
(
int
n
)
{
// only sum across procs one time
if
(
force_flag
==
0
)
{
MPI_Allreduce
(
ftotal
,
ftotal_all
,
3
,
MPI_DOUBLE
,
MPI_SUM
,
world
);
force_flag
=
1
;
}
return
ftotal_all
[
n
];
}
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