Perturbative universal state-selective correction for state-specific multi-reference coupled cluster methods

The State-Universal Multi-Reference Coupled-Cluster Theory: An Overview of Some Recent Advances

Some recent advances in the area of multi-reference coupled-cluster theory of the state-universal type are overviewed. An emphasis is placed on the following new developments: (i) the idea of combining the state-universal multi-reference coupled-cluster singles and doubles method (SUMRCCSD) with the multi-reference many-body perturbation theory (MRMBPT), in which cluster amplitudes of the SUMRC...

Four-Reference State-Specific Brillouin-Wigner Coupled- Cluster Method: Study of the IBr Molecule

We implemented the state-specific Brillouin–Wigner coupled-cluster method for the complete model space spanned by four reference configurations generated by two electrons in two active orbitals. We applied the method (together with the previously suggested a posteriori size-extensivity correction) to the calculation of spectroscopic constants of the IBr molecule, using averaged relativistic eff...

Scheduled Review Methods for Controllable State Variables

In many real systems in which a state variable should be controlled for being in appropriate range, the length of control (review) intervals is taken to be constant. In such systems, when the cost of reviews and out-of-range values of the state variable are considerable, this method may not be optimal. In this paper we let the length of review intervals to be variable during each operating cycl...

Variational formulation of perturbative explicitly-correlated coupled-cluster methods.

We present a variational formulation of the recently-proposed CCSD(2)(R12) method [Valeev, Phys. Chem. Chem. Phys., 2008, 10, 106]. The centerpiece of this approach is the CCSD(2)(R12) Lagrangian obtained via Löwdin partitioning of the coupled-cluster singles and doubles (CCSD) Hamiltonian. Extremization of the Lagrangian yields the second-order basis set incompleteness correction for the CCSD ...

Finite-State Methods for Spelling Correction