Abstract
Starting from the Hückel or SCF determinant Φ
0, a good approximation to a valence-correlated wavefunction is proposed by a simple exponential transformation of the components of Φ
I
on the various VB determinants Φ
I
, namely
Ψ
= Σ
I
|Φ
I
>exp (λ<Φ
I
|
H|Φ
I
>) <Φ|Φ
0 >. This single-parameter method, which was derived shown to be efficient for strongly correlated systems as well.