fix center(atoms) polymorphism

generation/Shells.jl

@@ -7,7 +7,7 @@ using PeriodicTable
 using Printf
 
 """Type of `GaussianBasis.BasisSet` parameters"""
-const Basis = Tuple{Atom, Vector{BasisFunction}}
+const Basis = Tuple{Vector{A}, Vector{S}} where {A<:Atom, S<:SphericalShell}
 
 """ 
     atom([Z, [xyz]])
@@ -47,8 +47,14 @@ Move a vector of atoms to a desired barycenter.
 
 All atoms are treated as mass 1.
 """
-function center(atoms::Vector{Molecules.Atom{T, X}}) where T<:Real where X<:Real
-    center(atoms, SVector{3, X}([0, 0, 0]))
+function center(atoms::Vector{<:Atom}, offset::SVector{3, <:Real}) 
+    ctr = sum(a.xyz for a in atoms) / length(atoms)
+    map(atoms) do a
+        move(a, offset - ctr)
+    end
+end
+function center(atoms::Vector{<:Atom})
+    center(atoms, SVector{3, Float64}([0, 0, 0]))
 end
 
 #--- Parse H atom once for all
@@ -65,5 +71,3 @@ end
 Base.show(io::IO, ::MIME"text/plain", at::Atom) = begin
     show(io, Molecules.string_repr(at))
 end
-
-