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chuckv |
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!=========================================================================== |
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! |
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!=========================================================================== |
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! . Subroutines: |
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! LANGEVIN_VERLET_DYNAMICS molecular dynamics using langevin |
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! dynamics |
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!=========================================================================== |
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module dynamics_langevin_verlet |
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use definitions, ONLY : DP,NDIM |
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use constants, ONLY : AMU_TO_KG,K_BOLTZ,MS_TO_AFS, & |
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KCALMOL_TO_AMUA2FS2, PI |
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use simulation |
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use parameter |
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use force_module, ONLY : calc_forces |
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use second_deriv |
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use force_utilities, ONLY : check |
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use status |
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! use velocity, ONLY : scale_velocities |
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use dynamics_utilities, ONLY : evolve_time, init_dynamics_loop, & |
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sim_status,DT2,DTSQRT,DTSQ2, init_status |
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use velocity, ONLY : calc_temp |
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#ifdef MPI |
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use mpi_module, ONLY : mpi_comm_world,mpi_err |
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#endif |
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implicit none |
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PRIVATE |
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SAVE |
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! . Constants common to langevin dynamcics |
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real ( kind = dp ) :: C0,C1,C2 |
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real ( kind = dp ), allocatable, dimension(:) :: CRV1,CRV2 |
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real ( kind = dp ), allocatable, dimension(:) :: FACR1,FACR2 |
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real ( kind = dp ), allocatable, dimension(:) :: FACV1,FACV2,FACV3 |
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real ( kind = dp ), allocatable, dimension(:) :: SDR,SDV |
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! . langevin arrays |
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real ( kind = dp ), allocatable, dimension(:,:) :: v_lang |
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real ( kind = dp ), allocatable, dimension(:) :: MASFAC |
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type (sim_status) :: langevin_status |
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public :: langevin_verlet_dynamics |
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contains |
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! . subroutine init_langevin sets up common |
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! constants for dynamics |
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subroutine init_langevin |
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use model_module, ONLY : get_max_atype |
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integer :: n_atypes_known |
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character(len=80) :: msg |
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real( kind = dp ) :: fact |
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real( kind = dp ) :: this_eta |
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! . allocate nlocal arrays |
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allocate(v_lang(ndim,nlocal)) |
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allocate(masfac(nlocal)) |
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! . find out how many atypes the simulation |
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! . knows about |
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n_atypes_known = get_max_atype() |
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allocate(SDR(n_atypes_known)) |
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allocate(SDV(n_atypes_known)) |
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allocate(CRV1(n_atypes_known)) |
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allocate(CRV2(n_atypes_known)) |
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allocate(FACR1(n_atypes_known)) |
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allocate(FACR2(n_atypes_known)) |
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allocate(FACV1(n_atypes_known)) |
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allocate(FACV2(n_atypes_known)) |
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allocate(FACV3(n_atypes_known)) |
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this_eta = eta |
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call calc_gamma_factors(this_eta) |
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! . Temperature and mass factors. |
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FACT = ( K_BOLTZ * bath_temp / AMU_TO_KG ) |
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!!!!!DANGER DANGER WILL |
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! WHERE ( .NOT. ATMFIX ) MASFAC = MS_TO_AFS * SQRT ( FACT / mass ) ! A fs^-1. |
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MASFAC = MS_TO_AFS * SQRT ( FACT / mass ) ! A fs^-1. |
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write(msg,*) "Visocity of solvent is: ", eta |
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call info("INIT_LANGEVIN",msg) |
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end subroutine init_langevin |
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subroutine langevin_verlet_dynamics() |
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use langevin_cluster_list, ONLY : init_langevin_list,create_langevin_list |
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logical :: update_nlist |
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logical :: do_pot |
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logical :: not_done |
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logical :: nmflag |
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integer :: step, i |
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real(kind = dp) :: temp |
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call init_status(langevin_status) |
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call init_dynamics_loop(langevin_status) |
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call init_langevin_list(nlocal) |
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! Start the main simulation loop. |
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do_pot = .true. |
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not_done = .true. |
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nmflag = .false. |
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step = 0 |
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!. initialize constants for dynamics |
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call init_langevin() |
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call create_langevin_list() |
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dynamics: do |
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if (.not.not_done) exit dynamics |
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step = step + 1 |
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! if (checktemp.and.(mod(step,check_temp_steps).eq.0)) then |
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! call calc_temp(langevin_status%temp) |
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! if (dabs(langevin_status%temp-target_temp).gt.therm_variance) then |
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! call scale_velocities(target_temp) |
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! end if |
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! end if |
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call check(update_nlist) |
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if (update_nlist) then |
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call create_langevin_list() |
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endif |
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call langevina() |
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! . Add in random forces |
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call RANDOM_FORCES |
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if (do_pot) then |
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call calc_forces(update_nlist,nmflag,pe = langevin_status%pot_e) |
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else |
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call calc_forces(update_nlist,nmflag) |
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endif |
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call langevinb() |
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call evolve_time(step,langevin_status,do_pot,not_done) |
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#ifdef MPI |
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call mpi_barrier(mpi_comm_world,mpi_err) |
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#endif |
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end do dynamics |
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deallocate(v_lang) |
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deallocate(masfac) |
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end subroutine langevin_verlet_dynamics |
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! . First part of langevin dynamics |
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! Advances positions from T to T + DT |
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! Advances velocities from T to T + DT/2 |
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!=================================== |
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subroutine langevina() |
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!=================================== |
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use langevin_cluster_list, ONLY : langevin_list |
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integer :: i |
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! units for time are femtosec (10^-15 sec) |
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! units for distance are angstroms (10^-10 m) |
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! units for velocity are angstroms femtosec^-1 |
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! units for mass are a.m.u. (1.661 * 10^-27 kg) |
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! units for force are kcal mol^-1 angstrom^-1 |
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! |
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! converter will put the final terms into angstroms. |
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! or angstrom/femtosecond. |
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! Calculate new positions and velocities |
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v_lang = 0.0_DP |
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do i = 1, nlocal |
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if (langevin_list(i)) then |
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q(1:ndim,i) = q(1:ndim,i) + & |
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FACR1(ident(i)) * v(1:ndim,i) + & |
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(FACR2(ident(i)) * f(1:ndim,i)/mass(i))*KCALMOL_TO_AMUA2FS2 |
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v_lang(1:ndim,i) = FACV1(ident(i)) * v(1:ndim,i) + & |
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(FACV2(ident(i)) * f(1:ndim,i)/mass(i)) * KCALMOL_TO_AMUA2FS2 |
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else |
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q(1:ndim,i) = q(1:ndim,i) + dt*v(1:ndim,i) & |
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+ (dtsq2*f(1:ndim,i)/mass(i))*KCALMOL_TO_AMUA2FS2 |
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v(1:ndim,i) = v(1:ndim,i) & |
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+ (dt2*f(1:ndim,i)/mass(i))*KCALMOL_TO_AMUA2FS2 |
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endif |
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end do |
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end subroutine langevina |
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!======================== |
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subroutine langevinb( ) |
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!========================= |
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use langevin_cluster_list, ONLY : langevin_list |
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integer :: i |
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! units for time are femtosec (10^-15 sec) |
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! units for distance are angstroms (10^-10 m) |
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! units for velocity are angstroms femtosec^-1 |
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! units for mass are a.m.u. (1.661 * 10^-27 kg) |
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! units for force are kcal mol^-1 angstrom^-1 |
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do i = 1, nlocal |
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if (langevin_list(i)) then |
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v(1:ndim,i) = v_lang(1:ndim,i) & |
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+ (FACV3(ident(i)) * f(1:ndim,i)/mass(i))*KCALMOL_TO_AMUA2FS2 |
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else ! standard movea |
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v(1:ndim,i) = v(1:ndim,i) & |
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+ (dt2*f(1:ndim,i)/mass(i))*KCALMOL_TO_AMUA2FS2 |
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endif |
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enddo |
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end subroutine langevinb |
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!----------------------- |
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SUBROUTINE RANDOM_FORCES |
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!----------------------- |
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use langevin_cluster_list, ONLY : langevin_list |
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use sprng_mod, ONLY : random_gauss |
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! . Local scalars. |
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INTEGER :: I, IATOM |
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REAL ( KIND = DP ) :: RANR, RANV, R1, R2 |
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! . Loop over the atoms. |
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DO IATOM = 1,nlocal |
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! . The atom is free. |
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IF ( langevin_list(iatom) ) THEN |
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! . Loop over the Cartesian components for the atom. |
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DO I = 1,ndim |
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! . Generate two Gaussian random numbers. |
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R1 = RANDOM_GAUSS ( ) |
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R2 = RANDOM_GAUSS ( ) |
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! . Calculate the position and velocity changes. |
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RANR = MASFAC(IATOM) * SDR(ident(iatom)) * R1 |
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RANV = MASFAC(IATOM) * SDV(ident(iatom)) * & |
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( CRV1(ident(iatom)) * R1 + CRV2(ident(iatom)) * R2 ) |
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! . Add in the components. |
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q(I,IATOM) = q(I,IATOM) + RANR |
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v_lang(I,IATOM) = v_lang(I,IATOM) + RANV |
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END DO |
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END IF |
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END DO |
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END SUBROUTINE RANDOM_FORCES |
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SUBROUTINE calc_gamma_factors(this_eta) |
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use model_module, ONLY : atype_mass,atype_identifier |
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integer :: atype, i |
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character(len = 80) :: msg |
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real( kind = dp ), intent(in) :: this_eta |
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real( kind = dp ) :: gamma |
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real( kind = dp ) :: FACT |
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real( kind = dp ) :: C0 |
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real( kind = dp ) :: C1 |
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real( kind = dp ) :: C2 |
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do i = 1, n_atypes_present |
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gamma = 0.0_DP |
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fact = 0.0_DP |
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C0 = 0.0_DP |
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C1 = 0.0_DP |
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C2 = 0.0_DP |
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atype = present_atypes(i) |
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!. calculate Gamma in fs^-1 |
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!. gamma = (6 * pi * atom sigma(angstroms) * viscosity(poise) * 100cm/m) * 1fs/10^-15sec / |
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!. (atom mass(amu) * amu_to_kg * 1000g/kg) |
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gamma = (6 * pi * get_langevin_sigma(atype) * this_eta ) / & |
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(atype_mass(atype)*amu_to_kg*10) * 1E-15_DP |
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write(msg,*) "Gamma for ",atype_identifier(atype), "is: ", gamma |
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call info("CALC_GAMMA_FACTORS",msg) |
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FACT = dt * gamma |
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C0 = EXP ( - FACT ) |
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C1 = ( 1.0_DP - C0 ) / FACT |
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C2 = ( 1.0_DP - C1 ) / FACT |
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! . Random force constants. |
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SDR(atype) = SQRT ( dt * dt * & |
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( 2.0_DP - ( 3.0_DP - 4.0_DP * C0 + C0 * C0 ) / FACT ) / FACT ) ! fs. |
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SDV(atype) = SQRT ( ( 1.0_DP - C0 * C0 ) ) ! Dimensionless. |
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CRV1(atype) = dt * ( 1.0_DP - C0 )**2 / ( FACT * SDR(atype) * SDV(atype) ) ! Dimensionless. |
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CRV2(atype) = SQRT ( 1.0_DP - CRV1(atype) * CRV1(atype) ) ! Dimensionless. |
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! . Calculate some integration constants. |
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FACR1(atype) = C1 * dt ! fs. |
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FACR2(atype) = C2 * dt * dt ! fs^2. |
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FACV1(atype) = C0 ! Dimensionless. |
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FACV2(atype) = ( C1 - C2 ) * dt ! fs. |
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FACV3(atype) = C2 * dt ! fs. |
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end do |
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END SUBROUTINE calc_gamma_factors |
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function get_langevin_sigma(this_atype) result(this_sigma) |
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integer, intent(in) :: this_atype |
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real( kind = dp ) :: this_sigma |
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include 'headers/atom.h' |
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select case (this_atype) |
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case(Au_atom) |
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this_sigma = 1.647E-10_DP |
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case(Ag_atom) |
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this_sigma = 1.574E-10_DP |
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case(Pt_atom) |
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this_sigma = 1.377E-10_DP |
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case(Pb_atom) |
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this_sigma = 2.148E-10_DP |
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case(Cu_atom) |
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this_sigma = 1.748E-10_DP |
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case(Ni_atom) |
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this_sigma = 1.417E-10_DP |
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case(Pd_atom) |
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this_sigma = 1.450E-10_DP |
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case default |
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call error("get_langevin_sigma","Unknown atom type") |
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end select |
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end function get_langevin_sigma |
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end module dynamics_langevin_verlet |
