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MMFF94: environment-dependent q⁰ for the O2CM terminal oxygen (type 107) — fixes spurious net charge on sulfones and related groups #186

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MMFF94: environment-dependent q⁰ for the O2CM terminal oxygen (type 107) — fixes spurious net charge on sulfones and related groups #186

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39 changes: 38 additions & 1 deletion source/kcharge.f
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Original file line number Diff line number Diff line change
Expand Up @@ -218,6 +218,7 @@ subroutine kchargem
integer i,j,k,m
integer it,kt,bt
integer ic,kc
integer nterm,koxo
real*8, allocatable :: pbase(:)
logical emprule
c
Expand All @@ -227,7 +228,43 @@ subroutine kchargem
do i = 1, n
it = type(i)
pchg(i) = 0.0d0
if (it .eq. 107) pchg(i) = -0.5d0
if (it .eq. 107) then
pchg(i) = -0.5d0
do j = 1, n12(i)
k = i12(j,i)
kt = type(k)
c the primary charge of a terminal oxygen follows the eq. (15)
c environment rule, q0 = -(n-k)/n: n is the number of terminal
c oxygens on the attached center, k counts the oxygens of the
c neutral parent oxyacid (1 for C, P and S(IV); 2 for N and
c tetracoordinate S(VI); 3 for Cl); neutral groups such as
c sulfones, nitro and phosphine oxides keep q0 = 0, their
c polarization living in the bond charge increments
koxo = -1
if (atomic(k) .eq. 6) koxo = 1
if (atomic(k) .eq. 15) koxo = 1
if (atomic(k) .eq. 7) koxo = 2
if (atomic(k) .eq. 17) koxo = 3
if (atomic(k) .eq. 16) then
koxo = 1
if (kt.eq.64 .or. kt.eq.65 .or. kt.eq.66 .or.
& kt.eq.68 .or. kt.eq.69 .or. kt.eq.70) koxo = 2
end if
if (koxo .gt. 0) then
nterm = 0
do m = 1, n12(k)
if (n12(i12(m,k)) .eq. 1) then
if (type(i12(m,k)).ge.107 .and.
& type(i12(m,k)).le.121) nterm = nterm + 1
end if
end do
pchg(i) = 0.0d0
if (nterm .gt. koxo) then
pchg(i) = -1.0d0*(nterm-koxo)/nterm
end if
end if
end do
end if
if (it .eq. 113) then
pchg(i) = 0.0d0
do j = 1, n12(i)
Expand Down