Orbital-optimized distinguishable cluster theory with explicit correlation.

A combination of orbital-optimized methods with explicit correlation is discussed for the example of the orbital-optimized distinguishable cluster approach. It is shown that the perturbative approach is applicable even in strongly correlated situations, and it is important in these cases to use Lagrange multipliers together with the amplitudes. The partial amplitude relaxation can be applied to relax the amplitudes and makes absolute energies closer to complete basis set results.