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! MTK (Martina Tuckerman and Klein) Nosie' Hoover chains |
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! See Molecular Physics, 1996, Vol. 87, No. 5, 1117-1157 for details of |
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! the algorithm. |
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! |
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! author: Charles F. Vardeman II |
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! date: 6-12-02 |
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! |
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! Interfaces: |
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! Called from dynamics module: |
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! public: nose_hoover_dynamics(): controls nose-hoover chains dynamics |
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! for the length of the simulation time: |
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! No Arguments: |
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|
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! private: |
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! nose_hoovera: updates nose_hoover chains and then advances particle positions and velocities |
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! by velocity verlet. |
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! nose_hooverb: updates velocities, second half of velocity verlet. and thermostat velocities and |
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! positions. |
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! init_hoover: initalize hoover structures |
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! apply_NHC_par: performs details of nose-hoover chains. |
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|
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|
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module dynamics_nose_hoover |
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use definitions, ONLY : DP,NDIM |
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use constants |
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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 force_utilities, ONLY : check |
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use velocity, ONLY : scale_velocities |
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use dynamics_utilities, ONLY : evolve_time, sim_status, init_dynamics_loop, & |
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DT2,DTSQRT,init_status |
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#ifdef MPI |
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use mpi_module, ONLY : mpi_allreduce,mpi_comm_world,mpi_err,& |
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mpi_double_precision, mpi_sum |
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#endif |
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|
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implicit none |
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PRIVATE |
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|
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|
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|
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public :: nose_hoover_dynamics |
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|
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type (sim_status) :: nose_status |
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|
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|
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contains |
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|
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|
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subroutine nose_hoover_dynamics() |
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use velocity, ONLY : calc_temp |
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|
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|
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|
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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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|
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integer :: step, i |
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|
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! initialize status (ke,pe,time, etc.) |
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call init_status(nose_status) |
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call init_dynamics_loop( nose_status ) |
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|
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! Start the main simulation loop. |
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|
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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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|
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dynamics: do |
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if (.not.not_done) exit dynamics |
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|
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step = step + 1 |
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|
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|
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if (checktemp.and.(mod(step,check_temp_steps).eq.0)) then |
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call calc_temp(nose_status%temp) |
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if (dabs(nose_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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|
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call nose_hoovera() |
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|
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call check(update_nlist) |
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|
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|
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if (do_pot) then |
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call calc_forces(update_nlist,nmflag,pe = nose_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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|
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|
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call nose_hooverb() |
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|
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call evolve_time(step,nose_status,do_pot,not_done) |
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|
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|
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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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|
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end subroutine nose_hoover_dynamics |
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|
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|
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! nose_hoovera(): advances velocities from T to T + DT/2 and positions from T to T + DT |
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subroutine nose_hoovera() |
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use velocity, ONLY : remove_cm_momentum,remove_angular_momentum |
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|
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|
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|
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|
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integer :: i, dim |
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real( kind = DP) :: ke, v2, instatemp, chi |
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real( kind = DP) :: kebar |
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|
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real( kind = DP ), dimension(ndim) :: v_dim_i |
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|
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real(kind=DP) :: ke_local |
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|
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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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|
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! converter = 1.0d0/2.390664d3 |
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|
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|
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! call nose_hoover chains |
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call apply_NHC_par() |
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|
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! advance velocities from t to t + dt/2 |
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do i = 1, nlocal |
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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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end do |
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|
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! advance positions from t to t+dt |
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do i = 1, nlocal |
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q(1:ndim,i) = q(1:ndim,i) + dt*v(1:ndim,i) |
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end do |
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|
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|
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end subroutine nose_hoovera |
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|
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|
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! advances velocities another half step from t+dt/2 to t + dt |
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subroutine nose_hooverb( ) |
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use velocity, ONLY : remove_cm_momentum,remove_angular_momentum |
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integer i |
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|
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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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do i = 1, nlocal |
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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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end do |
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|
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! apply nose-hoover thermostat |
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call apply_NHC_par() |
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|
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if (sim_type == "cluster") then |
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call remove_cm_momentum() |
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call remove_angular_momentum() |
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endif |
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end subroutine nose_hooverb |
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|
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|
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! does the Nose-Hoover part of the integration from t = 0 to t=DT/2 |
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! borrowed from Chris Fennel's code of thermostating |
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! by way of Hoover, Phys.Rev.A 1985, Vol.31 (3) 1695-1697 |
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|
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subroutine apply_NHC_par() |
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use velocity, ONLY : calc_temp |
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real(kind = DP) :: system_ke |
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real(kind = DP) :: system_temp |
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real(kind = DP) :: G_NkT |
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real(kind = DP) :: Q_mass |
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real(kind = DP) :: zeta |
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real(kind = DP) :: zetaScale |
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real(kind = DP),dimension(ndim) :: vi |
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|
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integer :: i |
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|
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call calc_temp(system_temp,system_ke) |
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|
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G_NkT = natoms*ndim*K_BOLTZ*target_temp |
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! and aren't the system_temp and system_ke similar to chris's kt and ke? |
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|
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! Q_mass is a function of the omega parameter |
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Q_mass = G_NkT / (omega * omega) |
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|
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! advance the zeta term to zeta(t + dt) |
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zeta = zeta + dt*((system_temp*2 - G_NkT)/Q_mass) |
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zetaScale = zeta * dt |
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|
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! perform thermostating on velocities and angular momenta |
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do i = 1, nlocal |
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vi(1:ndim) = v(1:ndim,i)*zetaScale |
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! similar thing here for our angular momenta |
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|
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v(1:ndim,i) = v(1:ndim,i) - vi(1:ndim) |
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! similar thing here for our angular momenta |
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enddo |
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|
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end subroutine apply_NHC_par |
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|
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|
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|
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!!$ ! other code borrowed from Chris Fennell's code of |
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!!$ ! G.J. Martyna et al. Mol. Phys., 1996, Vol. 87, No. 5, 1117-1157 |
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!!$ |
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!!$ subroutine apply_NHC_par() |
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!!$ use velocity, ONLY : calc_temp |
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!!$ real(kind = DP) :: scale |
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!!$ real(kind = DP) :: system_ke |
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!!$ real(kind = DP) :: system_temp |
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!!$ real(kind = DP) :: G_NkT |
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!!$ real(kind = DP) :: omega2 |
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!!$ real(kind = DP) :: value1, value2, value3, value4 |
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!!$ real(kind = DP) :: wdti2(n_ysval), wdti4(n_ysval), wdti8(n_ysval) |
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!!$ real(kind = DP) :: G_val(N_nos), vval(N_nos), xival(N_nos) |
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!!$ real(kind = DP) :: Q_mass |
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!!$ |
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!!$ integer :: i, j |
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!!$ |
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!!$ scale = 1._DP |
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!!$ |
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!!$ call calc_temp(system_temp,system_ke) |
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!!$ |
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!!$ G_NkT = natoms*ndim*K_BOLTZ*my_temp |
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!!$ |
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!!$ ! we need to get the w numbers for these values |
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!!$ ! but i think that chris has calculated the values |
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!!$ ! because they are values of constants |
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!!$ value1 = 0.67560359598d0 * dt |
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!!$ value2 = -0.85120719196d0 * dt |
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!!$ value3 = 0.207245385897d0 * dt |
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!!$ value4 = -0.328981543589d0 * dt |
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!!$ if (n_ysval.eq.3) then |
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!!$ wdti2(1) = value1 |
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!!$ wdti2(2) = value2 |
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!!$ wdti2(3) = value1 |
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!!$ wdti4(1) = 0.5_DP * wdti2(1) |
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!!$ wdti4(2) = 0.5_DP * wdti2(2) |
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!!$ wdti4(3) = wdti4(1) |
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!!$ wdti8(1) = 0.5_DP * wdti4(1) |
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!!$ wdti8(2) = 0.5_DP * wdti4(2) |
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!!$ wdti8(3) = wdti8(1) |
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!!$ else |
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!!$ write(*,*) 'Error: n_syval must be 3' |
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!!$ stop |
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!!$ endif |
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!!$ |
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!!$ omega2 = omega * omega |
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!!$ |
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!!$ ! set the Q_mass values |
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!!$ Q_mass(1) = G_NkT/omega2 |
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!!$ do i = 2, N_nos-1 |
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!!$ Q_mass(i) = system_temp/omega2 |
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!!$ enddo |
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!!$ |
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!!$ qmass(N_nos) = 2 * omega |
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!!$ |
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!!$ ! zero the intial xivals and vvals |
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!!$ do i = 1, N_nos |
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!!$ xival(i) = 0._DP |
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!!$ vval(i) = 0._DP |
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!!$ enddo |
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!!$ |
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!!$ ! Start the Nose_Hoover chain stepping |
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!!$ ! update the forces |
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!!$ G_val(1) = (system_ke - G_NkT)/Q_mass(1) |
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!!$ |
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!!$ ! start the multiple time stepping |
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!!$ do i = 1, n_cval |
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!!$ do j = 1, n_ysval |
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!!$ |
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!!$ ! update the thermostat velocities |
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!!$ vval(N_nos) = vval(N_nos) + G_val(N_nos)*wdti4(j)/i |
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!!$ do mcount = 1, N_nos-1 |
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!!$ aa = exp((-wdti8(j)/i) * vval((N_nos+1)-mcount)) |
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!!$ vval(N_nos-mcount) = vval(N_nos-mcount)*aa*aa & |
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!!$ + wdti4(j)*G_val(N_nos)*wdti4(j)/(i*i) |
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!!$ enddo |
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!!$ |
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!!$ ! update particle velocities |
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!!$ aa = exp((-wdti2(j)/i)*vval(1)) |
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!!$ scale = scale*aa |
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!!$ |
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!!$ ! update the forces |
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!!$ G_val(1) = (scale*scale*ke -G_NkT)/Q_mass(1) |
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!!$ |
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!!$ ! update the thermostat positions |
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!!$ do mcount = 1, N_nos-1 |
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!!$ xival(mcount) = xival(mcount) + vval(mcount)*(wdti2(j)/i) |
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!!$ enddo |
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!!$ |
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!!$ ! update the thermostat velocities |
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!!$ do mcount = 1, N_nos-1 |
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!!$ aa = exp((-wdti8(j)/i)*vval(mcount+1)) |
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!!$ vval(mcount) = vval(mcount)*aa*aa & |
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!!$ + (wdti4(j)/i)*G_val(mcount)*aa |
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!!$ G_val(mcount+1) = (Q_mass(mcount)*vval(mcount)*vval(mcount) & |
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!!$ - system_temp)/Q_mass(mcount+1) |
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!!$ enddo |
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!!$ |
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!!$ vval(N_nos) = vval(N_nos) + G_val(N_nos)*(wdti4(j)/i) |
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!!$ enddo |
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!!$ enddo |
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!!$ |
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!!$ ! scale both linear velocities and angular momenta |
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!!$ do i = 1, nlocal |
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!!$ v(1:ndim,i) = v(1:ndim,i)*scale |
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!!$ !something here for what we use for angular momenta |
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!!$ enddo |
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!!$ |
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!!$ end subroutine apply_NHC_par |
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|
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|
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|
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end module dynamics_nose_hoover |
