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module tblite_data_covrad
   use mctc_env, only : wp
   use mctc_io_convert, only : aatoau
   use mctc_io_symbols, only : to_number
   implicit none
   private

   public :: get_covalent_rad


   !> Covalent radii for DFT-D3 coordination number
   interface get_covalent_rad
      module procedure :: get_covalent_rad_num
      module procedure :: get_covalent_rad_sym
   end interface get_covalent_rad


   integer, parameter :: max_elem = 118

   !> Covalent radii (taken from Pyykko and Atsumi, Chem. Eur. J. 15, 2009,
   !  188-197), values for metals decreased by 10 %
   real(wp), parameter :: covalent_rad_2009(max_elem) = aatoau * [ &
      & 0.32_wp,0.46_wp, & ! H,He
      & 1.20_wp,0.94_wp,0.77_wp,0.75_wp,0.71_wp,0.63_wp,0.64_wp,0.67_wp, & ! Li-Ne
      & 1.40_wp,1.25_wp,1.13_wp,1.04_wp,1.10_wp,1.02_wp,0.99_wp,0.96_wp, & ! Na-Ar
      & 1.76_wp,1.54_wp, & ! K,Ca
      &                 1.33_wp,1.22_wp,1.21_wp,1.10_wp,1.07_wp, & ! Sc-
      &                 1.04_wp,1.00_wp,0.99_wp,1.01_wp,1.09_wp, & ! -Zn
      &                 1.12_wp,1.09_wp,1.15_wp,1.10_wp,1.14_wp,1.17_wp, & ! Ga-Kr
      & 1.89_wp,1.67_wp, & ! Rb,Sr
      &                 1.47_wp,1.39_wp,1.32_wp,1.24_wp,1.15_wp, & ! Y-
      &                 1.13_wp,1.13_wp,1.08_wp,1.15_wp,1.23_wp, & ! -Cd
      &                 1.28_wp,1.26_wp,1.26_wp,1.23_wp,1.32_wp,1.31_wp, & ! In-Xe
      & 2.09_wp,1.76_wp, & ! Cs,Ba
      &         1.62_wp,1.47_wp,1.58_wp,1.57_wp,1.56_wp,1.55_wp,1.51_wp, & ! La-Eu
      &         1.52_wp,1.51_wp,1.50_wp,1.49_wp,1.49_wp,1.48_wp,1.53_wp, & ! Gd-Yb
      &                 1.46_wp,1.37_wp,1.31_wp,1.23_wp,1.18_wp, & ! Lu-
      &                 1.16_wp,1.11_wp,1.12_wp,1.13_wp,1.32_wp, & ! -Hg
      &                 1.30_wp,1.30_wp,1.36_wp,1.31_wp,1.38_wp,1.42_wp, & ! Tl-Rn
      & 2.01_wp,1.81_wp, & ! Fr,Ra
      &      1.67_wp,1.58_wp,1.52_wp,1.53_wp,1.54_wp,1.55_wp,1.49_wp, & ! Ac-Am
      &      1.49_wp,1.51_wp,1.51_wp,1.48_wp,1.50_wp,1.56_wp,1.58_wp, & ! Cm-No
      &                 1.45_wp,1.41_wp,1.34_wp,1.29_wp,1.27_wp, & ! Lr-
      &                 1.21_wp,1.16_wp,1.15_wp,1.09_wp,1.22_wp, & ! -Cn
      &                 1.36_wp,1.43_wp,1.46_wp,1.58_wp,1.48_wp,1.57_wp ] ! Nh-Og

   !> D3 covalent radii used to construct the coordination number
   real(wp), parameter :: covalent_rad_d3(max_elem) = &
      & 4.0_wp / 3.0_wp * covalent_rad_2009

contains


!> Get covalent radius for a given element symbol
elemental function get_covalent_rad_sym(sym) result(rad)

   !> Element symbol
   character(len=*), intent(in) :: sym

   !> Covalent radius
   real(wp) :: rad

   rad = get_covalent_rad(to_number(sym))

end function get_covalent_rad_sym


!> Get covalent radius for a given atomic number
elemental function get_covalent_rad_num(num) result(rad)

   !> Atomic number
   integer, intent(in) :: num

   !> Covalent radius
   real(wp) :: rad

   if (num > 0 .and. num <= size(covalent_rad_d3)) then
      rad = covalent_rad_d3(num)
   else
      rad = 0.0_wp
   end if

end function get_covalent_rad_num


end module tblite_data_covrad
