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TABLE OF CONTENTS

• module response_step_mod
• procedure response_step_startup
• procedure ps_propagate
• procedure fftc_step
• procedure calc_exp_grid

response_step_mod

PURPOSE

    Integrator for the first-order perturbation theory for q(r,s).
    Propagates both q(r,s) and delq(r,s)

SOURCE

module response_step_mod
   use const_mod
   use chemistry_mod
   use fft_mod
 
   private
   public :: response_step_startup
   public :: fft_step
   public :: pspropagate
   public :: alloc_exparrays
   public :: calc_exparrays
   public :: calc_exp_grid
   public :: ps_propagate

response_step_startup

SUBROUTINE

    response_step_startup(ngrid,order)

PURPOSE

    Allocate the module variable exponential arrays

ARGUMENTS

    integer ngrid  - number of grid points
    integer order  - order of Richardson extrapolation

SOURCE

   subroutine response_step_startup(Ngrid, order)
   integer,intent(IN)  :: ngrid(3)
   integer,intent(IN)  :: order

ps_propagate

SUBROUTINE

    ps_propagate(plan,planc,ds,delqin,q0,exp_gpdotr,order,delta_omega, &
        monomer,p_mon,delqout,dsloc,qout)

PURPOSE

    Propagate q and delq by solving the inhomog pde. 
    call  fft_step and fftc_step for unperturbed and perturbation
    partition functions.

ARGUMENTS

    fft_plan planc      -  see fft_mod for details
    complex  delqin     -  delta q at beginning of the block
    complex  delqout    -  Output delta q array
    complex  exp_gpdotr -  exponential array of G.r for perturbation at G+k
     complex  f_inhomo  -  = d_w * q_0(1:2**order)
     integer  p_mon     -  index of the perturbed monomer
     integer  monomer   -  index of the monomer of the concerned chain site
                           over which the propagation is being implemented
     integer  order     -  order of extrapolation
     real     dsloc     -  contour step size for this block

SOURCE

   subroutine ps_propagate(delqin, delqout, p_mon, exp_gpdotr, &
                          f_inhomo, monomer, planc, order, dsloc) 
     
   complex(long), intent(IN)  :: delqin(:,:,:)
   complex(long), intent(OUT) :: delqout(:,:,:)
   complex(long), intent(IN)  :: exp_gpdotr(:,:,:)
   real(long),    intent(IN)  :: f_inhomo(:,:,:,:)
   integer,       intent(IN)  :: p_mon
   integer,       intent(IN)  :: monomer
   type(fft_plan)             :: planc
   real(long),    intent(IN)  :: dsloc
   integer,       intent(IN)  :: order

fftc_step

SUBROUTINE

    fftc_step(plan,order,q_in,q_out)

PURPOSE

    solve for perturbed partition function of one step
    call FFT and inverse FFT

ARGUMENTS

    fft_plan plan  -  see fft_mod for details
    integer order  -  extrapolation order
    real q_in      -  input partition
    real q_out     -  output partition

SOURCE

   subroutine fftc_step(plan,order,q_in,q_out)
   implicit none
   type(fft_plan), intent(IN)   :: plan
   integer,        intent(IN)   :: order
   complex(long),  intent(IN)   :: q_in(0:,0:,0:)
   complex(long), intent(OUT)   :: q_out(0:,0:,0:)

calc_exp_grid

SUBROUTINE

    calc_exp_grid(ksq_grid, ksq_grid_pert, omega_grid, 
                  monomer, ds, order, dsarray, pertb)

PURPOSE

    Calculate the module variable exponential arrays

ARGUMENTS

    real      ksq_grid  -  |G|^2 for reciprocal lattice vectors
    real    omega_grid  -  omega fields at grid points
    real ksq_grid_pert  -  |k+G|^2 on grids 
    integer    monomer  -  monomer type for block
    real            ds  -  chain step
    integer      order  -  order of extrapolation
    real       dsarray  -  output array that has stepsizes as elements
    logical      pertb  -  calculate the perturbed exponential if true

SOURCE

   subroutine calc_exp_grid(ksq_grid, ksq_grid_pert, omega_grid, &
                            monomer, ds, order, dsarray, pertb)
   implicit none
 
   real(long),  intent(IN) :: ksq_grid(:,:,:)
   real(long),  intent(IN) :: ksq_grid_pert(:,:,:)
   real(long),  intent(IN) :: omega_grid(:,:,:,:)
   integer,     intent(IN) :: monomer
   real(long),  intent(IN) :: ds
   integer,     intent(IN) :: order
   real(long), intent(out) :: dsarray(:)
   logical,     intent(IN) :: pertb