My new paper with Matthias Hanuer, Andreas Köhn, and Jürgen Gauss has just appeared in JCP. The significant contribution of this work is to introduce a new wave function for the internally contracted MRCC method based on a sequential transformation of the reference function (sqic-MRCC). The sqic-MRCC wave function has the form:
where is a multiconfigurational wave function.
Sequencing the exponential operator leads to an advantageous similarity-transformed Hamiltonian, which in turn leads to equations that are less complex with respect to the ic-MRCC method. What’s most amazing is the fact that the ic-MRCC and sqic-MRCC methods yield almost identical energies.