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!! Calculates Long Range forces Lennard-Jones interactions. |
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!! Corresponds to the force field defined in lj_FF.cpp |
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!! @author Charles F. Vardeman II |
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!! @author Matthew Meineke |
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!! @version $Id: calc_LJ_FF.F90,v 1.2 2003-03-10 19:26:45 chuckv Exp $, $Date: 2003-03-10 19:26:45 $, $Name: not supported by cvs2svn $, $Revision: 1.2 $ |
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module lj_ff |
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use simulation |
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use definitions |
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use generic_lists |
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#ifdef IS_MPI |
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use mpiSimulation |
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#endif |
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implicit none |
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PRIVATE |
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!! Logical has lj force field module been initialized? |
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logical, save :: isljFFinit = .false. |
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!! Public methods and data |
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public :: getLjPot |
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public :: init_ljFF |
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type :: lj_mixed_params |
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!! Mass of Particle |
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real ( kind = dp ) :: mass = 0.0_dp |
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!! Lennard-Jones epslon |
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real ( kind = dp ) :: epsilon = 0.0_dp |
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!! Lennard-Jones Sigma |
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real ( kind = dp ) :: sigma = 0.0_dp |
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!! Lennard-Jones Sigma Squared |
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real ( kind = dp ) :: sigma2 = 0.0_dp |
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!! Lennard-Jones Sigma to sixth |
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real ( kind = dp ) :: sigma6 = 0.0_dp |
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end type lj_mixed_params |
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type (lj_mixed_params), dimension(:,:) :: ljMixed |
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contains |
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subroutine init_ljFF(ListHead,status) |
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type (atype),pointer :: ListHead |
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integer :: nTypes |
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integer, intent(out) :: status |
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integer :: myStatus |
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status = 0 |
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call createMixingList(ListHead,myStatus) |
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if (myStatus /= 0) then |
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status = -1 |
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return |
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end if |
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end subroutine init_ljFF |
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subroutine createMixingList(ListHead,status) |
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type (atype), pointer :: ListHead |
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integer :: listSize |
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integer :: status |
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integer :: i |
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integer :: j |
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integer :: i = 0 |
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integer :: j = 0 |
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type (atype), pointer :: tmpPtr_i => null() |
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type (atype), pointer :: tmpPtr_j => null() |
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status = 0 |
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listSize = getListLen(ListHead) |
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if (listSize == 0) then |
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status = -1 |
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return |
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end if |
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if (.not. associated(ljMixed)) then |
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allocate(ljMixed(listSize,listSize)) |
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else |
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status = -1 |
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return |
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end if |
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tmpPtr_i => ListHead |
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tmpPtr_j => tmpPtr_i%next |
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do while (associated(tmpPtr_i)) |
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i = i + 1 |
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! do self mixing rule |
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ljMixed(i,i)%sigma = tmpPtr_i%sigma |
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ljMixed(i,i)%sigma2 = (ljMixed(i,i)%sigma) ** 2 |
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ljMixed(i,i)%sigma6 = (ljMixed(i,i)%sigma) ** 6 |
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ljMixed(i,i)%epsilon = tmpPtr_i%epsilon |
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j = i + 1 |
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do while (associated(tmpPtr_j)) |
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ljMixed(i,j)%sigma = & |
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calcLJMix("sigma",tmpPtr_i%sigma, & |
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tmpPtr_j%sigma) |
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ljMixed(i,j)%sigma2 = & |
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(ljMixed(i,j)%sigma)**2 |
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ljMixed(i,j)%sigma6 = & |
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(ljMixed(i,j)%sigma)**6 |
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ljMixed(i,j)%epsilon = & |
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calcLJMix("epsilon",tmpPtr_i%epsilon, & |
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tmpPtr_j%epsilon) |
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ljMixed(j,i)%sigma = ljMixed(i,j)%sigma |
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ljMixed(j,i)%sigma2 = ljMixed(i,j)%sigma2 |
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ljMixed(j,i)%sigma6 = ljMixed(i,j)%sigma6 |
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ljMixed(j,i)%epsilon = ljMixed(i,j)%epsilon |
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tmpPtr_j => tmpPtr_j%next |
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j = j + 1 |
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end do |
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! advance pointers |
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tmpPtr_i => tmpPtr_i%next |
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if (associated(tmpPtr_i)) then |
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tmpPtr_j => tmpPtr_i%next |
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endif |
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end do |
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end subroutine createMixingList |
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!! Calculates the potential between two lj particles based on two lj_atype pointers, optionally returns second |
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!! derivatives. |
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subroutine getLjForce(r,pot,dudr,atype1,atype2,d2,status) |
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! arguments |
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!! Length of vector between particles |
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real( kind = dp ), intent(in) :: r |
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!! Potential Energy |
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real( kind = dp ), intent(out) :: pot |
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!! Derivatve wrt postion |
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real( kind = dp ), intent(out) :: dudr |
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!! Second Derivative, optional, used mainly for normal mode calculations. |
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real( kind = dp ), intent(out), optional :: d2 |
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type (atype), pointer :: atype1 |
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type (atype), pointer :: atype2 |
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integer, intent(out), optional :: status |
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! local Variables |
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real( kind = dp ) :: sigma |
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real( kind = dp ) :: sigma2 |
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real( kind = dp ) :: sigma6 |
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real( kind = dp ) :: epsilon |
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real( kind = dp ) :: rcut |
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real( kind = dp ) :: rcut2 |
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real( kind = dp ) :: rcut6 |
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real( kind = dp ) :: r2 |
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real( kind = dp ) :: r6 |
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real( kind = dp ) :: t6 |
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real( kind = dp ) :: t12 |
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real( kind = dp ) :: tp6 |
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real( kind = dp ) :: tp12 |
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real( kind = dp ) :: delta |
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logical :: doSec = .false. |
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integer :: errorStat |
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!! Optional Argument Checking |
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! Check to see if we need to do second derivatives |
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if (present(d2)) doSec = .true. |
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if (present(status)) status = 0 |
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! Look up the correct parameters in the mixing matrix |
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sigma = ljMixed(atype1%atype_ident,atype2%atype_ident)%sigma |
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sigma2 = ljMixed(atype1%atype_ident,atype2%atype_ident)%sigma2 |
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sigma6 = ljMixed(atype1%atype_ident,atype2%atype_ident)%sigma6 |
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epsilon = ljMixed(atype1%atype_ident,atype2%atype_ident)%epsilon |
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call getRcut(rcut,rcut2=rcut2,rcut6=rcut6,status=errorStat) |
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r2 = r * r |
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r6 = r2 * r2 * r2 |
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t6 = sigma6/ r6 |
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t12 = t6 * t6 |
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tp6 = sigma6 / rcut6 |
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tp12 = tp6*tp6 |
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delta = -4.0E0_DP*epsilon * (tp12 - tp6) |
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if (r.le.rcut) then |
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pot = 4.0E0_DP * epsilon * (t12 - t6) + delta |
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dudr = 24.0E0_DP * epsilon * (t6 - 2.0E0_DP*t12) / r |
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if(doSec) d2 = 24.0E0_DP * epsilon * (26.0E0_DP*t12 - 7.0E0_DP*t6)/r/r |
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else |
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pot = 0.0E0_DP |
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dudr = 0.0E0_DP |
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if(doSec) d2 = 0.0E0_DP |
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endif |
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return |
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end subroutine getLJForce |
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!! Calculates the mixing for sigma or epslon based on character string for initialzition of mixing array. |
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function calcLJMix(thisParam,param1,param2,status) result(myMixParam) |
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character(len=*) :: thisParam |
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real(kind = dp) :: param1 |
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real(kind = dp) :: param2 |
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real(kind = dp ) :: myMixParam |
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character(len = getStringLen()) :: thisMixingRule |
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integer, optional :: status |
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!! get the mixing rules from the simulation |
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thisMixingRule = returnMixingRules() |
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myMixParam = 0.0_dp |
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if (present(status)) status = 0 |
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select case (thisMixingRule) |
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case ("standard") |
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select case (thisParam) |
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case ("sigma") |
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myMixParam = 0.5_dp * (param1 + param2) |
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case ("epsilon") |
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myMixParam = sqrt(param1 * param2) |
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case default |
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status = -1 |
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end select |
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case("LJglass") |
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case default |
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status = -1 |
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end select |
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end function calcLJMix |
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end module lj_ff |
