A Weaker Geminal Product Wave Function Ansatz

2D-Block Geminals: a non 1-orthogonal and non 0-seniority model with reduced computational complexity

We present a new geminal product wave function ansatz where the geminals are not constrained to be strongly orthogonal nor to be of seniority zero.Instead, we introduce weaker orthogonality constraints between geminals whichsignificantly lower the computational effort, without sacrificing the indistinguishability of the electrons.With this simplified ansatz for geminals, the number of terms in the calculation of the matrix elements of quantum observables isconsiderably reduced.A proof of principle is reported and confirms that the ansatz is more accurate than strongly orthogonal geminal products while remaining computationally affordable.