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fix_rhok.cpp
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rLAMMPS lammps
fix_rhok.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: Ulf R. Pedersen, ulf@urp.dk
------------------------------------------------------------------------- */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include "fix_rhok.h"
#include "atom.h"
#include "domain.h"
#include "error.h"
#include "force.h"
#include "respa.h"
#include "update.h"
#include "citeme.h"
using
namespace
LAMMPS_NS
;
using
namespace
FixConst
;
static
const
char
cite_fix_rhok
[]
=
"Bias on the collective density field (fix rhok):
\n\n
"
"@Article{pedersen_jcp139_104102_2013,
\n
"
"title = {Direct calculation of the solid-liquid Gibbs free energy difference in a single equilibrium simulation},
\n
"
"volume = {139},
\n
"
"number = {10},
\n
"
"url = {http://aip.scitation.org/doi/10.1063/1.4818747},
\n
"
"doi = {10.1063/1.4818747},
\n
"
"urldate = {2017-10-03},
\n
"
"journal = {J. Chem. Phys.},
\n
"
"author = {Pedersen, Ulf R.},
\n
"
"year = {2013},
\n
"
"pages = {104102}
\n
"
"}
\n\n
"
;
FixRhok
::
FixRhok
(
LAMMPS
*
inLMP
,
int
inArgc
,
char
**
inArgv
)
:
Fix
(
inLMP
,
inArgc
,
inArgv
)
{
if
(
lmp
->
citeme
)
lmp
->
citeme
->
add
(
cite_fix_rhok
);
// Check arguments
if
(
inArgc
!=
8
)
error
->
all
(
FLERR
,
"Illegal fix rhoKUmbrella command"
);
// Set up fix flags
scalar_flag
=
1
;
// have compute_scalar
vector_flag
=
1
;
// have compute_vector...
size_vector
=
3
;
// ...with this many components
global_freq
=
1
;
// whose value can be computed at every timestep
thermo_energy
=
1
;
// this fix changes system's potential energy
extscalar
=
0
;
// but the deltaPE might not scale with # of atoms
extvector
=
0
;
// neither do the components of the vector
// Parse fix options
int
n
[
3
];
n
[
0
]
=
force
->
inumeric
(
FLERR
,
inArgv
[
3
]);
n
[
1
]
=
force
->
inumeric
(
FLERR
,
inArgv
[
4
]);
n
[
2
]
=
force
->
inumeric
(
FLERR
,
inArgv
[
5
]);
mK
[
0
]
=
n
[
0
]
*
(
2
*
M_PI
/
(
domain
->
boxhi
[
0
]
-
domain
->
boxlo
[
0
]));
mK
[
1
]
=
n
[
1
]
*
(
2
*
M_PI
/
(
domain
->
boxhi
[
1
]
-
domain
->
boxlo
[
1
]));
mK
[
2
]
=
n
[
2
]
*
(
2
*
M_PI
/
(
domain
->
boxhi
[
2
]
-
domain
->
boxlo
[
2
]));
mKappa
=
force
->
numeric
(
FLERR
,
inArgv
[
6
]);
mRhoK0
=
force
->
numeric
(
FLERR
,
inArgv
[
7
]);
}
// Methods that this fix implements
// --------------------------------
// Tells LAMMPS where this fix should act
int
FixRhok
::
setmask
()
{
int
mask
=
0
;
// This fix modifies forces...
mask
|=
POST_FORCE
;
mask
|=
POST_FORCE_RESPA
;
mask
|=
MIN_POST_FORCE
;
// ...and potential energies
mask
|=
THERMO_ENERGY
;
return
mask
;
}
// Initializes the fix at the beginning of a run
void
FixRhok
::
init
()
{
// RESPA boilerplate
if
(
strcmp
(
update
->
integrate_style
,
"respa"
)
==
0
)
mNLevelsRESPA
=
((
Respa
*
)
update
->
integrate
)
->
nlevels
;
// Count the number of affected particles
int
nThisLocal
=
0
;
int
*
mask
=
atom
->
mask
;
int
nlocal
=
atom
->
nlocal
;
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
{
// Iterate through all atoms on this CPU
if
(
mask
[
i
]
&
groupbit
)
{
// ...only those affected by this fix
nThisLocal
++
;
}
}
MPI_Allreduce
(
&
nThisLocal
,
&
mNThis
,
1
,
MPI_INT
,
MPI_SUM
,
world
);
mSqrtNThis
=
sqrt
(
mNThis
);
}
// Initial application of the fix to a system (when doing MD)
void
FixRhok
::
setup
(
int
inVFlag
)
{
if
(
strcmp
(
update
->
integrate_style
,
"verlet"
)
==
0
)
post_force
(
inVFlag
);
else
{
((
Respa
*
)
update
->
integrate
)
->
copy_flevel_f
(
mNLevelsRESPA
-
1
);
post_force_respa
(
inVFlag
,
mNLevelsRESPA
-
1
,
0
);
((
Respa
*
)
update
->
integrate
)
->
copy_f_flevel
(
mNLevelsRESPA
-
1
);
}
}
// Initial application of the fix to a system (when doing minimization)
void
FixRhok
::
min_setup
(
int
inVFlag
)
{
post_force
(
inVFlag
);
}
// Modify the forces calculated in the main force loop of ordinary MD
void
FixRhok
::
post_force
(
int
inVFlag
)
{
double
**
x
=
atom
->
x
;
double
**
f
=
atom
->
f
;
int
*
mask
=
atom
->
mask
;
int
nlocal
=
atom
->
nlocal
;
// Loop over locally-owned atoms affected by this fix and calculate the
// partial rhoK's
mRhoKLocal
[
0
]
=
0.0
;
mRhoKLocal
[
1
]
=
0.0
;
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
{
// Iterate through all atoms on this CPU
if
(
mask
[
i
]
&
groupbit
)
{
// ...only those affected by this fix
// rho_k = sum_i exp( - i k.r_i )
mRhoKLocal
[
0
]
+=
cos
(
mK
[
0
]
*
x
[
i
][
0
]
+
mK
[
1
]
*
x
[
i
][
1
]
+
mK
[
2
]
*
x
[
i
][
2
]
);
mRhoKLocal
[
1
]
-=
sin
(
mK
[
0
]
*
x
[
i
][
0
]
+
mK
[
1
]
*
x
[
i
][
1
]
+
mK
[
2
]
*
x
[
i
][
2
]
);
}
}
// Now calculate mRhoKGlobal
MPI_Allreduce
(
mRhoKLocal
,
mRhoKGlobal
,
2
,
MPI_DOUBLE
,
MPI_SUM
,
world
);
// Info: < \sum_{i,j} e^{-ik.(r_i - r_j)} > ~ N, so
// we define rho_k as (1 / sqrt(N)) \sum_i e^{-i k.r_i}, so that
// <rho_k^2> is intensive.
mRhoKGlobal
[
0
]
/=
mSqrtNThis
;
mRhoKGlobal
[
1
]
/=
mSqrtNThis
;
// We'll need magnitude of rho_k
double
rhoK
=
sqrt
(
mRhoKGlobal
[
0
]
*
mRhoKGlobal
[
0
]
+
mRhoKGlobal
[
1
]
*
mRhoKGlobal
[
1
]
);
for
(
int
i
=
0
;
i
<
nlocal
;
i
++
)
{
// Iterate through all atoms on this CPU
if
(
mask
[
i
]
&
groupbit
)
{
// ...only those affected by this fix
// Calculate forces
// U = kappa/2 ( |rho_k| - rho_k^0 )^2
// f_i = -grad_i U = -kappa ( |rho_k| - rho_k^0 ) grad_i |rho_k|
// grad_i |rho_k| = Re( rho_k* (-i k e^{-i k . r_i} / sqrt(N)) ) / |rho_k|
//
// In terms of real and imag parts of rho_k,
//
// Re( rho_k* (-i k e^{-i k . r_i}) ) =
// (- Re[rho_k] * sin( k . r_i ) - Im[rho_k] * cos( k . r_i )) * k
double
sinKRi
=
sin
(
mK
[
0
]
*
x
[
i
][
0
]
+
mK
[
1
]
*
x
[
i
][
1
]
+
mK
[
2
]
*
x
[
i
][
2
]
);
double
cosKRi
=
cos
(
mK
[
0
]
*
x
[
i
][
0
]
+
mK
[
1
]
*
x
[
i
][
1
]
+
mK
[
2
]
*
x
[
i
][
2
]
);
double
prefactor
=
mKappa
*
(
rhoK
-
mRhoK0
)
/
rhoK
*
(
-
mRhoKGlobal
[
0
]
*
sinKRi
-
mRhoKGlobal
[
1
]
*
cosKRi
)
/
mSqrtNThis
;
f
[
i
][
0
]
-=
prefactor
*
mK
[
0
];
f
[
i
][
1
]
-=
prefactor
*
mK
[
1
];
f
[
i
][
2
]
-=
prefactor
*
mK
[
2
];
}
}
}
// Forces in RESPA loop
void
FixRhok
::
post_force_respa
(
int
inVFlag
,
int
inILevel
,
int
inILoop
)
{
if
(
inILevel
==
mNLevelsRESPA
-
1
)
post_force
(
inVFlag
);
}
// Forces in minimization loop
void
FixRhok
::
min_post_force
(
int
inVFlag
)
{
post_force
(
inVFlag
);
}
// Compute the change in the potential energy induced by this fix
double
FixRhok
::
compute_scalar
()
{
double
rhoK
=
sqrt
(
mRhoKGlobal
[
0
]
*
mRhoKGlobal
[
0
]
+
mRhoKGlobal
[
1
]
*
mRhoKGlobal
[
1
]
);
return
0.5
*
mKappa
*
(
rhoK
-
mRhoK0
)
*
(
rhoK
-
mRhoK0
);
}
// Compute the ith component of the vector
double
FixRhok
::
compute_vector
(
int
inI
)
{
if
(
inI
==
0
)
return
mRhoKGlobal
[
0
];
// Real part
else
if
(
inI
==
1
)
return
mRhoKGlobal
[
1
];
// Imagniary part
else
if
(
inI
==
2
)
return
sqrt
(
mRhoKGlobal
[
0
]
*
mRhoKGlobal
[
0
]
+
mRhoKGlobal
[
1
]
*
mRhoKGlobal
[
1
]
);
else
return
12345.0
;
}
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