mirror of https://gitlab.com/QEF/q-e.git
81 lines
2.3 KiB
Fortran
81 lines
2.3 KiB
Fortran
! dftd3 program for computing the dispersion energy and forces from cart
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! and atomic numbers as described in
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!
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! S. Grimme, J. Antony, S. Ehrlich and H. Krieg
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! J. Chem. Phys, 132 (2010), 154104
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!
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! S. Grimme, S. Ehrlich and L. Goerigk, J. Comput. Chem, 32 (2011), 1456
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! (for BJ-damping)
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!
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! Copyright (C) 2009 - 2011 Stefan Grimme, University of Muenster, Germany
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!
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! Repackaging of the original code without any change in the functionality:
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!
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! Copyright (C) 2016, Bálint Aradi
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!
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! This program is free software; you can redistribute it and/or modify
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! it under the terms of the GNU General Public License as published by
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! the Free Software Foundation; either version 1, or (at your option)
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! any later version.
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!
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! This program is distributed in the hope that it will be useful,
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! but WITHOUT ANY WARRANTY; without even the implied warranty of
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! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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! GNU General Public License for more details.
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!
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! For the GNU General Public License, see <http://www.gnu.org/licenses/>
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!
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module dftd3_common
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implicit none
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! Working precision (double precision)
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integer, parameter :: wp = kind(1.0d0)
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! Large integers
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integer, parameter :: int64 = selected_int_kind(12)
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! global ad hoc parameters
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real(wp), parameter :: k1 = 16.0
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real(wp), parameter :: k2 = 4./3.
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! reasonable choices are between 3 and 5
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! this gives smoth curves with maxima around the integer values
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! k3=3 give for CN=0 a slightly smaller value than computed
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! for the free atom. This also yields to larger CN for atoms
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! in larger molecules but with the same chem. environment
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! which is physically not right
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! values >5 might lead to bumps in the potential
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real(wp), parameter :: k3 = -4.
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real(wp), parameter :: autoang = 0.52917720859_wp ! aligned to NIST data
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real(wp), parameter :: autokcal = 627.509541d0
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real(wp), parameter :: autoev = 27.21138505
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! J/mol nm^6 - > au
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real(wp), parameter :: c6conv = 1.d-3/2625.4999d0/((autoang / 10.0d0)**6)
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contains
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subroutine limit(iat,jat,iadr,jadr)
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integer iat,jat,iadr,jadr,i
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iadr=1
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jadr=1
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i=100
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10 if (iat.gt.100) then
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iat=iat-100
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iadr=iadr+1
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goto 10
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end if
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i=100
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20 if (jat.gt.100) then
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jat=jat-100
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jadr=jadr+1
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goto 20
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end if
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end subroutine limit
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end module dftd3_common
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