taper_types.F

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!--------------------------------------------------------------------------------------------------!
!   CP2K: A general program to perform molecular dynamics simulations                              !
!   Copyright 2000-2025 CP2K developers group <https://cp2k.org>                                   !
!                                                                                                  !
!   SPDX-License-Identifier: GPL-2.0-or-later                                                      !
!--------------------------------------------------------------------------------------------------!
 
! **************************************************************************************************
!> \brief Definition of the semi empirical parameter types.
!> \author Teodoro Laino [tlaino] - 10.2008 University of Zurich
! **************************************************************************************************
MODULE taper_types
 
   USE kinds,                           ONLY: dp
#include "./base/base_uses.f90"
 
   IMPLICIT NONE
 
   PRIVATE
 
   ! *** Global parameters ***
 
   CHARACTER(len=*), PARAMETER, PRIVATE :: moduleN = 'taper_types'
 
! **************************************************************************************************
!> \brief Taper type
! **************************************************************************************************
   TYPE taper_type
      LOGICAL                               :: apply_taper = .false.
      REAL(kind=dp)                         :: r0 = -1.0_dp, rscale = -1.0_dp
   END TYPE taper_type
 
   PUBLIC :: taper_type, taper_create, taper_release, taper_eval, dtaper_eval
 
CONTAINS
 
! **************************************************************************************************
!> \brief Creates taper type
!> \param taper ...
!> \param rc ...
!> \param range ...
! **************************************************************************************************
   SUBROUTINE taper_create(taper, rc, range)
      TYPE(taper_type), POINTER                          :: taper
      REAL(kind=dp), INTENT(IN)                          :: rc, range
 
      cpassert(.NOT. ASSOCIATED(taper))
      ALLOCATE (taper)
      IF (range > epsilon(0.0_dp)) THEN
         taper%apply_taper = .true.
         cpassert(range > 0.0_dp)
         taper%r0 = 2.0_dp*rc - 20.0_dp*range
         taper%rscale = 1.0_dp/range
      ELSE
         taper%apply_taper = .false.
      END IF
 
   END SUBROUTINE taper_create
 
! **************************************************************************************************
!> \brief Releases taper type
!> \param taper ...
! **************************************************************************************************
   SUBROUTINE taper_release(taper)
      TYPE(taper_type), POINTER                          :: taper
 
      IF (ASSOCIATED(taper)) THEN
         DEALLOCATE (taper)
      END IF
   END SUBROUTINE taper_release
 
! **************************************************************************************************
!> \brief Taper functions
!> \param taper ...
!> \param rij ...
!> \return ...
! **************************************************************************************************
   FUNCTION taper_eval(taper, rij) RESULT(ft)
      TYPE(taper_type), POINTER                          :: taper
      REAL(kind=dp), INTENT(IN)                          :: rij
      REAL(kind=dp)                                      :: ft
 
      REAL(kind=dp)                                      :: dr
 
      ft = 1._dp
      IF (taper%apply_taper) THEN
         dr = taper%rscale*(rij - taper%r0)
         ft = 0.5_dp*(1.0_dp - tanh(dr))
      END IF
   END FUNCTION taper_eval
 
! **************************************************************************************************
!> \brief Analytical derivatives for taper function
!> \param taper ...
!> \param rij ...
!> \return ...
! **************************************************************************************************
   FUNCTION dtaper_eval(taper, rij) RESULT(dft)
      TYPE(taper_type), POINTER                          :: taper
      REAL(kind=dp), INTENT(IN)                          :: rij
      REAL(kind=dp)                                      :: dft
 
      REAL(kind=dp)                                      :: dr
 
      dft = 0.0_dp
      IF (taper%apply_taper) THEN
         dr = taper%rscale*(rij - taper%r0)
         dft = -0.5_dp*(1.0_dp - tanh(dr)**2)*taper%rscale
      END IF
   END FUNCTION dtaper_eval
 
END MODULE taper_types