| 1 |
mmeineke |
377 |
subroutine v_constrain_a(dt,natoms,mass,rx,ry,rz, & |
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vx,vy,vz,fx,fy,fz, n_constrained, constraints_sqr, c_i, c_j, & |
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box_x, box_y, box_z) |
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implicit none |
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! ******************************************************************* |
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! ** FIRST PART OF VELOCITY VERLET ALGORITHM ** |
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! ** ** |
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! ** USAGE: ** |
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! ** ** |
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! ** THE FIRST PART OF THE ALGORITHM IS A TAYLOR SERIES WHICH ** |
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! ** ADVANCES POSITIONS FROM T TO T + DT AND VELOCITIES FROM ** |
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! ** T TO T + DT/2. AFTER THIS, THE FORCE ROUTINE IS CALLED. ** |
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! ******************************************************************* |
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! move part a calculate velocities |
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INTEGER I |
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double precision DT2, DTSQ2 |
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double precision box_x, box_y, box_z |
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! Global Parameters |
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INTEGER maxn,ndim,max_dim |
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parameter (maxn=2048,ndim=3,max_dim=3) |
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INTEGER natoms |
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! Global arrays |
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double precision mass(natoms) |
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double precision RX(natoms), RY(natoms), RZ(natoms) !Position |
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double precision VX(natoms), VY(natoms), VZ(natoms) !Velocity |
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double precision FX(natoms), FY(natoms), FZ(natoms) !force |
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! Paramaters for force subroutines |
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double precision dt |
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! variables for the constraint methods |
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integer n_constrained |
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integer c_i(n_constrained), c_j(n_constrained) |
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double precision constraints_sqr(n_constrained) |
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logical done |
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logical moving(natoms), moved(natoms) |
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double precision rptol, tol, tol2 |
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double precision pxab, pyab, pzab, pabsq, rabsq, diffsq |
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double precision rxab, ryab, rzab, rpab, gab |
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double precision dx, dy, dz, rma, rmb |
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integer a, b, it, maxit |
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parameter (rptol = 1.0d-6, tol = 1.0d-6 ) |
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parameter ( maxit = 100 ) |
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double precision px(natoms), py(natoms), pz(natoms) |
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double precision e_convert |
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parameter ( e_convert = 4.184d-4 ) |
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chuckv |
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mmeineke |
377 |
DT2 = DT / 2.0d0 |
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DTSQ2 = DT * DT2 |
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DO I = 1, natoms |
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px(I) = RX(I) + DT * VX(I) + & |
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(DTSQ2 * FX(I) * e_convert / mass(i)) |
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py(I) = RY(I) + DT * VY(I) + & |
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(DTSQ2 * FY(I) * e_convert / mass(i)) |
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pz(I) = RZ(I) + DT * VZ(I) + & |
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(DTSQ2 * FZ(I) * e_convert / mass(i)) |
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VX(I) = VX(I) + (DT2 * FX(I) * e_convert / mass(i)) |
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VY(I) = VY(I) + (DT2 * FY(I) * e_convert / mass(i)) |
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VZ(I) = VZ(I) + (DT2 * FZ(I) * e_convert / mass(i)) |
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moving(i) = .false. |
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moved(i) = .true. |
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end do |
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it = 0 |
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done = .false. |
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! start iterative loop |
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do while( (.not. done) .and. (it .le. maxit)) |
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done = .true. |
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do i = 1, n_constrained |
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a = c_i(i) |
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b = c_j(i) |
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if( moved(a) .or. moved(b) ) then |
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pxab = px(a) - px(b) |
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pyab = py(a) - py(b) |
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pzab = pz(a) - pz(b) |
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pxab = pxab - box_x * dsign( 1.0d0, pxab ) & |
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* int( dabs( pxab / box_x ) + 0.5d0 ) |
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pyab = pyab - box_y * dsign( 1.0d0, pyab ) & |
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* int( dabs( pyab / box_y ) + 0.5d0 ) |
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pzab = pzab - box_z * dsign( 1.0d0, pzab ) & |
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* int( dabs( pzab / box_z ) + 0.5d0 ) |
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pabsq = pxab * pxab + pyab * pyab + pzab * pzab |
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rabsq = constraints_sqr(i) |
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diffsq = rabsq - pabsq |
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! write ( *,* )diffsq |
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if( dabs(diffsq) .gt. tol ) then |
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rxab = rx(a) - rx(b) |
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ryab = ry(a) - ry(b) |
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rzab = rz(a) - rz(b) |
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rxab = rxab - box_x * dsign( 1.0d0, rxab ) & |
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* int( dabs( rxab / box_x ) + 0.5d0 ) |
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ryab = ryab - box_y * dsign( 1.0d0, ryab ) & |
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* int( dabs( ryab / box_y ) + 0.5d0 ) |
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rzab = rzab - box_z * dsign( 1.0d0, rzab ) & |
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* int( dabs( rzab / box_z ) + 0.5d0 ) |
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| 128 |
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rpab = rxab * pxab + ryab * pyab + rzab * pzab |
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if( dabs(rpab) .lt. ( rabsq * rptol ) ) then |
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write (*, '('' Constraint Failure '')' ) |
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write (*,*) a-1, b-1,rpab, rabsq * rptol |
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stop |
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end if |
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rma = 1.0d0 / mass(a) |
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rmb = 1.0d0 / mass(b) |
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gab = diffsq / ( 2.0d0 * ( rma + rmb ) * rpab ) |
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dx = rxab * gab |
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dy = ryab * gab |
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dz = rzab * gab |
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px(a) = px(a) + rma * dx |
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py(a) = py(a) + rma * dy |
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pz(a) = pz(a) + rma * dz |
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| 148 |
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px(b) = px(b) - rmb * dx |
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py(b) = py(b) - rmb * dy |
| 150 |
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pz(b) = pz(b) - rmb * dz |
| 151 |
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| 152 |
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dx = dx / dt |
| 153 |
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dy = dy / dt |
| 154 |
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dz = dz / dt |
| 155 |
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| 156 |
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vx(a) = vx(a) + rma * dx |
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vy(a) = vy(a) + rma * dy |
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vz(a) = vz(a) + rma * dz |
| 159 |
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| 160 |
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vx(b) = vx(b) - rmb * dx |
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vy(b) = vy(b) - rmb * dy |
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vz(b) = vz(b) - rmb * dz |
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moving(a) = .true. |
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moving(b) = .true. |
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done = .false. |
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endif |
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endif |
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enddo |
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do i = 1, natoms |
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moved(i) = moving(i) |
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moving(i) = .false. |
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enddo |
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it = it + 1 |
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enddo |
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! end of iterative loop |
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if( .not. done) then |
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write (*, '('' too many constraint iterations in move_a '')' ) |
| 185 |
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stop |
| 186 |
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endif |
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! store new values |
| 189 |
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| 190 |
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do i = 1, natoms |
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rx(i) = px(i) |
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ry(i) = py(i) |
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rz(i) = pz(i) |
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enddo |
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RETURN |
| 199 |
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end subroutine v_constrain_a |
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| 201 |
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Subroutine v_constrain_b(dt,natoms,mass,rx,ry,rz, & |
| 202 |
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vx,vy,vz,fx,fy,fz,k, n_constrained, constraints_sqr, & |
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c_i, c_j, box_x, box_y, box_z) |
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implicit none |
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! ******************************************************************* |
| 207 |
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! ** SECOND PART OF VELOCITY VERLET ALGORITHM ** |
| 208 |
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! ** ** |
| 209 |
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! ** USAGE: ** |
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! ** ** |
| 211 |
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! ** THE SECOND PART OF THE ALGORITHM ADVANCES VELOCITIES FROM ** |
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! ** T + DT/2 TO T + DT. THIS ASSUMES THAT FORCES HAVE BEEN ** |
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! ** COMPUTED IN THE FORCE ROUTINE AND STORED IN FX, FY, FZ. ** |
| 214 |
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! ******************************************************************* |
| 215 |
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| 216 |
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! declarations |
| 217 |
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| 218 |
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integer i |
| 219 |
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double precision accvel2, dt2 |
| 220 |
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double precision box_x, box_y, box_z |
| 221 |
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| 222 |
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! Global Parameters |
| 223 |
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| 224 |
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| 225 |
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INTEGER natoms |
| 226 |
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| 227 |
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! Global arrays |
| 228 |
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| 229 |
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double precision mass(natoms) |
| 230 |
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double precision RX(natoms), RY(natoms), RZ(natoms) !position |
| 231 |
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double precision VX(natoms), VY(natoms), VZ(natoms) !velocity |
| 232 |
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double precision FX(natoms), FY(natoms), FZ(natoms) !force |
| 233 |
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| 234 |
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| 235 |
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! Declaration for the kinetic energy |
| 236 |
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| 237 |
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double precision k |
| 238 |
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| 239 |
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! Paramaters for force subroutines |
| 240 |
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| 241 |
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double precision dt |
| 242 |
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| 243 |
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! constraint parameters and variables |
| 244 |
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| 245 |
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double precision tol, rxab, ryab, rzab, gab |
| 246 |
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| 247 |
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double precision vxab, vyab, vzab, dx, dy, dz, rma, rmb, rvab |
| 248 |
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integer a, b, it, maxit, n_constrained |
| 249 |
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parameter ( maxit = 100 ) |
| 250 |
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logical done |
| 251 |
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logical moving(natoms), moved(natoms) |
| 252 |
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integer c_i(n_constrained), c_j(n_constrained) |
| 253 |
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double precision constraints_sqr(n_constrained) |
| 254 |
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| 255 |
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double precision e_convert |
| 256 |
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parameter ( e_convert = 4.184d-4 ) |
| 257 |
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| 258 |
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| 259 |
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! ******************************************************************* |
| 260 |
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| 261 |
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tol = 1.0d-6 / dt |
| 262 |
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dt2 = dt / 2.0d0 |
| 263 |
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accvel2 = 0.0d0 |
| 264 |
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k = 0.0d0 |
| 265 |
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DO i = 1, natoms |
| 266 |
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| 267 |
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VX(I) = VX(I) + (DT2 * FX(I) * e_convert / mass(i)) |
| 268 |
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VY(I) = VY(I) + (DT2 * FY(I) * e_convert / mass(i)) |
| 269 |
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VZ(I) = VZ(I) + (DT2 * FZ(I) * e_convert / mass(i)) |
| 270 |
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| 271 |
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moving(i) = .false. |
| 272 |
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moved(i) = .true. |
| 273 |
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enddo |
| 274 |
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| 275 |
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it = 0 |
| 276 |
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done = .false. |
| 277 |
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| 278 |
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do while( (.not. done) .and. ( it .le. maxit) ) |
| 279 |
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| 280 |
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done = .true. |
| 281 |
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| 282 |
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do i=1, n_constrained |
| 283 |
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| 284 |
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a = c_i(i) |
| 285 |
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b = c_j(i) |
| 286 |
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| 287 |
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if( moved(a) .or. moved(b) ) then |
| 288 |
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| 289 |
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vxab = vx(a) - vx(b) |
| 290 |
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vyab = vy(a) - vy(b) |
| 291 |
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vzab = vz(a) - vz(b) |
| 292 |
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| 293 |
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rxab = rx(a) - rx(b) |
| 294 |
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ryab = ry(a) - ry(b) |
| 295 |
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rzab = rz(a) - rz(b) |
| 296 |
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| 297 |
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rxab = rxab - box_x * dsign( 1.0d0, rxab ) & |
| 298 |
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* int( dabs( rxab / box_x ) + 0.5d0 ) |
| 299 |
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ryab = ryab - box_y * dsign( 1.0d0, ryab ) & |
| 300 |
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* int( dabs( ryab / box_y ) + 0.5d0 ) |
| 301 |
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rzab = rzab - box_z * dsign( 1.0d0, rzab ) & |
| 302 |
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* int( dabs( rzab / box_z ) + 0.5d0 ) |
| 303 |
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| 304 |
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| 305 |
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rma = 1.0d0 / mass(a) |
| 306 |
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rmb = 1.0d0 / mass(b) |
| 307 |
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| 308 |
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rvab = rxab * vxab + ryab * vyab + rzab * vzab |
| 309 |
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| 310 |
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gab = -rvab / ( ( rma + rmb ) * constraints_sqr(i) ) |
| 311 |
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| 312 |
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if ( dabs(gab) .gt. tol) then |
| 313 |
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| 314 |
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dx = rxab * gab |
| 315 |
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dy = ryab * gab |
| 316 |
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dz = rzab * gab |
| 317 |
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| 318 |
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vx(a) = vx(a) + rma * dx |
| 319 |
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vy(a) = vy(a) + rma * dy |
| 320 |
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vz(a) = vz(a) + rma * dz |
| 321 |
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| 322 |
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vx(b) = vx(b) - rmb * dx |
| 323 |
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vy(b) = vy(b) - rmb * dy |
| 324 |
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vz(b) = vz(b) - rmb * dz |
| 325 |
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| 326 |
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moving(a) = .true. |
| 327 |
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moving(b) = .true. |
| 328 |
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done = .false. |
| 329 |
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| 330 |
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endif |
| 331 |
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| 332 |
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endif |
| 333 |
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| 334 |
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enddo |
| 335 |
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| 336 |
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do i = 1, natoms |
| 337 |
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| 338 |
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moved(i) = moving(i) |
| 339 |
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moving(i) = .false. |
| 340 |
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| 341 |
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enddo |
| 342 |
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| 343 |
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it = it + 1 |
| 344 |
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| 345 |
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enddo |
| 346 |
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| 347 |
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! End of iterative loop |
| 348 |
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| 349 |
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if (.not. done) then |
| 350 |
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| 351 |
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write(*, '('' Too many constraint iterations in moveb '')') |
| 352 |
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stop |
| 353 |
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| 354 |
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endif |
| 355 |
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| 356 |
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do i = 1, natoms |
| 357 |
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| 358 |
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accvel2 = VX(I) ** 2 + VY(I) ** 2 + VZ(I) ** 2 |
| 359 |
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k = k + 0.5d0 * mass(i) * accvel2 / e_convert |
| 360 |
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| 361 |
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end do |
| 362 |
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| 363 |
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| 364 |
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end subroutine v_constrain_b |
