information:highlighting
Approximation methods

The proper wave function then must be composed of the symmetric (+) and antisymmetric(−) linear combinations: ψ ± (0) (r 1, r 2) = 1 2 (ψ a (r 1) ψ b (r 2) ± ψ a (r 2) ψ b (r 1)) {\displaystyle \psi _{\pm }^{(0)}(\mathbf {r} _{1}\,,\mathbf {r} _{2})={\frac {1}{\sqrt {2}}}(\psi _{a}(\mathbf {r} _{1})\psi _{b}(\mathbf {r} _{2})\pm \psi _{a}(\mathbf {r} _{2})\psi _{b}(\mathbf {r} _{1}))} or for the special cases of ψ a = ψ b {\displaystyle \psi _{a}=\psi _{b}} (both electrons have identical quantum numbers, parahelium only): ψ + (0) = ψ a (r 1) ψ a (r 2) {\displaystyle \psi _{+}^{(0)}=\psi _{a}(\mathbf {r} _{1})\psi _{a}(\mathbf {r} _{2})}.