| 1 |
subroutine v_constrain_a(dt,natoms,mass,rx,ry,rz, & |
| 2 |
vx,vy,vz,fx,fy,fz, n_constrained, constraints_sqr, c_i, c_j, & |
| 3 |
box_x, box_y, box_z) |
| 4 |
implicit none |
| 5 |
|
| 6 |
! ******************************************************************* |
| 7 |
! ** FIRST PART OF VELOCITY VERLET ALGORITHM ** |
| 8 |
! ** ** |
| 9 |
! ** USAGE: ** |
| 10 |
! ** ** |
| 11 |
! ** THE FIRST PART OF THE ALGORITHM IS A TAYLOR SERIES WHICH ** |
| 12 |
! ** ADVANCES POSITIONS FROM T TO T + DT AND VELOCITIES FROM ** |
| 13 |
! ** T TO T + DT/2. AFTER THIS, THE FORCE ROUTINE IS CALLED. ** |
| 14 |
! ******************************************************************* |
| 15 |
|
| 16 |
|
| 17 |
! move part a calculate velocities |
| 18 |
|
| 19 |
INTEGER I |
| 20 |
double precision DT2, DTSQ2 |
| 21 |
|
| 22 |
double precision box_x, box_y, box_z |
| 23 |
|
| 24 |
! Global Parameters |
| 25 |
|
| 26 |
INTEGER maxn,ndim,max_dim |
| 27 |
parameter (maxn=2048,ndim=3,max_dim=3) |
| 28 |
INTEGER natoms |
| 29 |
|
| 30 |
! Global arrays |
| 31 |
|
| 32 |
double precision mass(natoms) |
| 33 |
double precision RX(natoms), RY(natoms), RZ(natoms) !Position |
| 34 |
double precision VX(natoms), VY(natoms), VZ(natoms) !Velocity |
| 35 |
double precision FX(natoms), FY(natoms), FZ(natoms) !force |
| 36 |
|
| 37 |
! Paramaters for force subroutines |
| 38 |
|
| 39 |
double precision dt |
| 40 |
|
| 41 |
! variables for the constraint methods |
| 42 |
|
| 43 |
integer n_constrained |
| 44 |
integer c_i(n_constrained), c_j(n_constrained) |
| 45 |
double precision constraints_sqr(n_constrained) |
| 46 |
logical done |
| 47 |
logical moving(natoms), moved(natoms) |
| 48 |
double precision rptol, tol, tol2 |
| 49 |
double precision pxab, pyab, pzab, pabsq, rabsq, diffsq |
| 50 |
double precision rxab, ryab, rzab, rpab, gab |
| 51 |
double precision dx, dy, dz, rma, rmb |
| 52 |
integer a, b, it, maxit |
| 53 |
parameter (rptol = 1.0d-6, tol = 1.0d-6 ) |
| 54 |
parameter ( maxit = 100 ) |
| 55 |
|
| 56 |
double precision px(natoms), py(natoms), pz(natoms) |
| 57 |
|
| 58 |
double precision e_convert |
| 59 |
parameter ( e_convert = 4.184d-4 ) |
| 60 |
|
| 61 |
|
| 62 |
write(*,*) 'n_constrained = ', n_constrained |
| 63 |
|
| 64 |
DT2 = DT / 2.0d0 |
| 65 |
DTSQ2 = DT * DT2 |
| 66 |
|
| 67 |
DO I = 1, natoms |
| 68 |
|
| 69 |
px(I) = RX(I) + DT * VX(I) + & |
| 70 |
(DTSQ2 * FX(I) * e_convert / mass(i)) |
| 71 |
py(I) = RY(I) + DT * VY(I) + & |
| 72 |
(DTSQ2 * FY(I) * e_convert / mass(i)) |
| 73 |
pz(I) = RZ(I) + DT * VZ(I) + & |
| 74 |
(DTSQ2 * FZ(I) * e_convert / mass(i)) |
| 75 |
VX(I) = VX(I) + (DT2 * FX(I) * e_convert / mass(i)) |
| 76 |
VY(I) = VY(I) + (DT2 * FY(I) * e_convert / mass(i)) |
| 77 |
VZ(I) = VZ(I) + (DT2 * FZ(I) * e_convert / mass(i)) |
| 78 |
|
| 79 |
moving(i) = .false. |
| 80 |
moved(i) = .true. |
| 81 |
|
| 82 |
end do |
| 83 |
|
| 84 |
it = 0 |
| 85 |
done = .false. |
| 86 |
|
| 87 |
! start iterative loop |
| 88 |
|
| 89 |
do while( (.not. done) .and. (it .le. maxit)) |
| 90 |
|
| 91 |
done = .true. |
| 92 |
|
| 93 |
do i = 1, n_constrained |
| 94 |
|
| 95 |
a = c_i(i) |
| 96 |
b = c_j(i) |
| 97 |
|
| 98 |
if( moved(a) .or. moved(b) ) then |
| 99 |
|
| 100 |
pxab = px(a) - px(b) |
| 101 |
pyab = py(a) - py(b) |
| 102 |
pzab = pz(a) - pz(b) |
| 103 |
|
| 104 |
pxab = pxab - box_x * dsign( 1.0d0, pxab ) & |
| 105 |
* int( dabs( pxab / box_x ) + 0.5d0 ) |
| 106 |
pyab = pyab - box_y * dsign( 1.0d0, pyab ) & |
| 107 |
* int( dabs( pyab / box_y ) + 0.5d0 ) |
| 108 |
pzab = pzab - box_z * dsign( 1.0d0, pzab ) & |
| 109 |
* int( dabs( pzab / box_z ) + 0.5d0 ) |
| 110 |
|
| 111 |
|
| 112 |
pabsq = pxab * pxab + pyab * pyab + pzab * pzab |
| 113 |
rabsq = constraints_sqr(i) |
| 114 |
diffsq = rabsq - pabsq |
| 115 |
! write ( *,* )diffsq |
| 116 |
|
| 117 |
if( dabs(diffsq) .gt. tol ) then |
| 118 |
|
| 119 |
rxab = rx(a) - rx(b) |
| 120 |
ryab = ry(a) - ry(b) |
| 121 |
rzab = rz(a) - rz(b) |
| 122 |
|
| 123 |
rxab = rxab - box_x * dsign( 1.0d0, rxab ) & |
| 124 |
* int( dabs( rxab / box_x ) + 0.5d0 ) |
| 125 |
ryab = ryab - box_y * dsign( 1.0d0, ryab ) & |
| 126 |
* int( dabs( ryab / box_y ) + 0.5d0 ) |
| 127 |
rzab = rzab - box_z * dsign( 1.0d0, rzab ) & |
| 128 |
* int( dabs( rzab / box_z ) + 0.5d0 ) |
| 129 |
|
| 130 |
rpab = rxab * pxab + ryab * pyab + rzab * pzab |
| 131 |
|
| 132 |
if( dabs(rpab) .lt. ( rabsq * rptol ) ) then |
| 133 |
write (*, '('' Constraint Failure '')' ) |
| 134 |
write (*,*) a-1, b-1,rpab, rabsq * rptol |
| 135 |
stop |
| 136 |
end if |
| 137 |
|
| 138 |
rma = 1.0d0 / mass(a) |
| 139 |
rmb = 1.0d0 / mass(b) |
| 140 |
|
| 141 |
gab = diffsq / ( 2.0d0 * ( rma + rmb ) * rpab ) |
| 142 |
dx = rxab * gab |
| 143 |
dy = ryab * gab |
| 144 |
dz = rzab * gab |
| 145 |
|
| 146 |
px(a) = px(a) + rma * dx |
| 147 |
py(a) = py(a) + rma * dy |
| 148 |
pz(a) = pz(a) + rma * dz |
| 149 |
|
| 150 |
px(b) = px(b) - rmb * dx |
| 151 |
py(b) = py(b) - rmb * dy |
| 152 |
pz(b) = pz(b) - rmb * dz |
| 153 |
|
| 154 |
dx = dx / dt |
| 155 |
dy = dy / dt |
| 156 |
dz = dz / dt |
| 157 |
|
| 158 |
vx(a) = vx(a) + rma * dx |
| 159 |
vy(a) = vy(a) + rma * dy |
| 160 |
vz(a) = vz(a) + rma * dz |
| 161 |
|
| 162 |
vx(b) = vx(b) - rmb * dx |
| 163 |
vy(b) = vy(b) - rmb * dy |
| 164 |
vz(b) = vz(b) - rmb * dz |
| 165 |
|
| 166 |
moving(a) = .true. |
| 167 |
moving(b) = .true. |
| 168 |
done = .false. |
| 169 |
|
| 170 |
endif |
| 171 |
endif |
| 172 |
|
| 173 |
enddo |
| 174 |
|
| 175 |
do i = 1, natoms |
| 176 |
moved(i) = moving(i) |
| 177 |
moving(i) = .false. |
| 178 |
enddo |
| 179 |
|
| 180 |
it = it + 1 |
| 181 |
enddo |
| 182 |
|
| 183 |
! end of iterative loop |
| 184 |
|
| 185 |
if( .not. done) then |
| 186 |
write (*, '('' too many constraint iterations in move_a '')' ) |
| 187 |
stop |
| 188 |
endif |
| 189 |
|
| 190 |
! store new values |
| 191 |
|
| 192 |
do i = 1, natoms |
| 193 |
rx(i) = px(i) |
| 194 |
ry(i) = py(i) |
| 195 |
rz(i) = pz(i) |
| 196 |
enddo |
| 197 |
|
| 198 |
|
| 199 |
|
| 200 |
RETURN |
| 201 |
end subroutine v_constrain_a |
| 202 |
|
| 203 |
Subroutine v_constrain_b(dt,natoms,mass,rx,ry,rz, & |
| 204 |
vx,vy,vz,fx,fy,fz,k, n_constrained, constraints_sqr, & |
| 205 |
c_i, c_j, box_x, box_y, box_z) |
| 206 |
implicit none |
| 207 |
|
| 208 |
! ******************************************************************* |
| 209 |
! ** SECOND PART OF VELOCITY VERLET ALGORITHM ** |
| 210 |
! ** ** |
| 211 |
! ** USAGE: ** |
| 212 |
! ** ** |
| 213 |
! ** THE SECOND PART OF THE ALGORITHM ADVANCES VELOCITIES FROM ** |
| 214 |
! ** T + DT/2 TO T + DT. THIS ASSUMES THAT FORCES HAVE BEEN ** |
| 215 |
! ** COMPUTED IN THE FORCE ROUTINE AND STORED IN FX, FY, FZ. ** |
| 216 |
! ******************************************************************* |
| 217 |
|
| 218 |
! declarations |
| 219 |
|
| 220 |
integer i |
| 221 |
double precision accvel2, dt2 |
| 222 |
double precision box_x, box_y, box_z |
| 223 |
|
| 224 |
! Global Parameters |
| 225 |
|
| 226 |
|
| 227 |
INTEGER natoms |
| 228 |
|
| 229 |
! Global arrays |
| 230 |
|
| 231 |
double precision mass(natoms) |
| 232 |
double precision RX(natoms), RY(natoms), RZ(natoms) !position |
| 233 |
double precision VX(natoms), VY(natoms), VZ(natoms) !velocity |
| 234 |
double precision FX(natoms), FY(natoms), FZ(natoms) !force |
| 235 |
|
| 236 |
|
| 237 |
! Declaration for the kinetic energy |
| 238 |
|
| 239 |
double precision k |
| 240 |
|
| 241 |
! Paramaters for force subroutines |
| 242 |
|
| 243 |
double precision dt |
| 244 |
|
| 245 |
! constraint parameters and variables |
| 246 |
|
| 247 |
double precision tol, rxab, ryab, rzab, gab |
| 248 |
|
| 249 |
double precision vxab, vyab, vzab, dx, dy, dz, rma, rmb, rvab |
| 250 |
integer a, b, it, maxit, n_constrained |
| 251 |
parameter ( maxit = 100 ) |
| 252 |
logical done |
| 253 |
logical moving(natoms), moved(natoms) |
| 254 |
integer c_i(n_constrained), c_j(n_constrained) |
| 255 |
double precision constraints_sqr(n_constrained) |
| 256 |
|
| 257 |
double precision e_convert |
| 258 |
parameter ( e_convert = 4.184d-4 ) |
| 259 |
|
| 260 |
|
| 261 |
! ******************************************************************* |
| 262 |
|
| 263 |
tol = 1.0d-6 / dt |
| 264 |
dt2 = dt / 2.0d0 |
| 265 |
accvel2 = 0.0d0 |
| 266 |
k = 0.0d0 |
| 267 |
DO i = 1, natoms |
| 268 |
|
| 269 |
VX(I) = VX(I) + (DT2 * FX(I) * e_convert / mass(i)) |
| 270 |
VY(I) = VY(I) + (DT2 * FY(I) * e_convert / mass(i)) |
| 271 |
VZ(I) = VZ(I) + (DT2 * FZ(I) * e_convert / mass(i)) |
| 272 |
|
| 273 |
moving(i) = .false. |
| 274 |
moved(i) = .true. |
| 275 |
enddo |
| 276 |
|
| 277 |
it = 0 |
| 278 |
done = .false. |
| 279 |
|
| 280 |
do while( (.not. done) .and. ( it .le. maxit) ) |
| 281 |
|
| 282 |
done = .true. |
| 283 |
|
| 284 |
do i=1, n_constrained |
| 285 |
|
| 286 |
a = c_i(i) |
| 287 |
b = c_j(i) |
| 288 |
|
| 289 |
if( moved(a) .or. moved(b) ) then |
| 290 |
|
| 291 |
vxab = vx(a) - vx(b) |
| 292 |
vyab = vy(a) - vy(b) |
| 293 |
vzab = vz(a) - vz(b) |
| 294 |
|
| 295 |
rxab = rx(a) - rx(b) |
| 296 |
ryab = ry(a) - ry(b) |
| 297 |
rzab = rz(a) - rz(b) |
| 298 |
|
| 299 |
rxab = rxab - box_x * dsign( 1.0d0, rxab ) & |
| 300 |
* int( dabs( rxab / box_x ) + 0.5d0 ) |
| 301 |
ryab = ryab - box_y * dsign( 1.0d0, ryab ) & |
| 302 |
* int( dabs( ryab / box_y ) + 0.5d0 ) |
| 303 |
rzab = rzab - box_z * dsign( 1.0d0, rzab ) & |
| 304 |
* int( dabs( rzab / box_z ) + 0.5d0 ) |
| 305 |
|
| 306 |
|
| 307 |
rma = 1.0d0 / mass(a) |
| 308 |
rmb = 1.0d0 / mass(b) |
| 309 |
|
| 310 |
rvab = rxab * vxab + ryab * vyab + rzab * vzab |
| 311 |
|
| 312 |
gab = -rvab / ( ( rma + rmb ) * constraints_sqr(i) ) |
| 313 |
|
| 314 |
if ( dabs(gab) .gt. tol) then |
| 315 |
|
| 316 |
dx = rxab * gab |
| 317 |
dy = ryab * gab |
| 318 |
dz = rzab * gab |
| 319 |
|
| 320 |
vx(a) = vx(a) + rma * dx |
| 321 |
vy(a) = vy(a) + rma * dy |
| 322 |
vz(a) = vz(a) + rma * dz |
| 323 |
|
| 324 |
vx(b) = vx(b) - rmb * dx |
| 325 |
vy(b) = vy(b) - rmb * dy |
| 326 |
vz(b) = vz(b) - rmb * dz |
| 327 |
|
| 328 |
moving(a) = .true. |
| 329 |
moving(b) = .true. |
| 330 |
done = .false. |
| 331 |
|
| 332 |
endif |
| 333 |
|
| 334 |
endif |
| 335 |
|
| 336 |
enddo |
| 337 |
|
| 338 |
do i = 1, natoms |
| 339 |
|
| 340 |
moved(i) = moving(i) |
| 341 |
moving(i) = .false. |
| 342 |
|
| 343 |
enddo |
| 344 |
|
| 345 |
it = it + 1 |
| 346 |
|
| 347 |
enddo |
| 348 |
|
| 349 |
! End of iterative loop |
| 350 |
|
| 351 |
if (.not. done) then |
| 352 |
|
| 353 |
write(*, '('' Too many constraint iterations in moveb '')') |
| 354 |
stop |
| 355 |
|
| 356 |
endif |
| 357 |
|
| 358 |
do i = 1, natoms |
| 359 |
|
| 360 |
accvel2 = VX(I) ** 2 + VY(I) ** 2 + VZ(I) ** 2 |
| 361 |
k = k + 0.5d0 * mass(i) * accvel2 / e_convert |
| 362 |
|
| 363 |
end do |
| 364 |
|
| 365 |
|
| 366 |
end subroutine v_constrain_b |
