Search for: [Abstract = "We investigate the performance of two approaches to remedy the notorious instability problems on explicitly correlated multi\-reference averaged coupled\-pair functional \(r12\-MR\-ACPF\) level of theory for the cases of HF molecule and Ne dimer. These two approaches are\: i\) the restriction of the unitary orbital invariance while retaining a chemically meaningful ansatz\; ii\) the contraction of associated r12\-terms to geminals using amplitudes from the first\-order perturbation theory wavefunction. We observe that our modifications outperform the extremal pair approach, which is commonly used on explicitly correlated coupled\-cluster \(CC\-R12\) level of theory and conclude that using geminals, which are e.g. taken from the first\-order Mřller\-Plesset perturbation theory wavefunction instead, might be a better choice."]
