Jeziorski-Monkhorst ansatz

The Hilbert space multireference CC (see e.g. Refs. [36-40]), based on the Jeziorski-Monkhorst ansatz for the wave operator [36]. This ansatz can be either combined with the standard (Rayleigh-Schrodinger) Bloch equation, or with the Brillouin-Wigner Bloch equation (cf. Section 18.4), or with a linear combination of both... 

The Ansatz we have chosen for our unitary group-based MRCC methods [45-48] is designed to closely mimic the Jeziorski-Monkhorst (JM) Ansatz [51, 83] in order to follow quite closely the developments in the analogous non-spin-adapted theories. As mentioned, we choose a set of Gel fand states, 0, to denote the model functions. We next introduce our spin-free JM-inspired Ansatz in Eq. (10) for the wave operator acting on 0 s. Our choice differs in two aspects from the traditional spinorbital-based JM... 

In this subsection, we sketch the essence of SSMRPT2, " which is derived from the quasi-linearized form of the parent state-specific multireference coupled cluster (SSMRCC) theory (also known as MkMRCC theory in the literature). The Jeziorski-Monkhorst (JM) ansatz for the wavefunction is adopted in the parent SSMRCC theory ... 

Substituting the Jeziorski-Monkhorst cluster ansatz (4.78) into eqn. (4.58), leads to the following cluster expansion for the exact wave function... 

So far, we have specified the wave operator H in the BW form (15). If we adopt an exponential ansatz for the wave operator Cl, we can speak about the single-root multireference Brillouin-Wigner coupled-cluster (MR BWCC) theory. The simplest way how to accomplish the idea of an exponential expansion is to exploit the so-called state universal or Hilbert space exponential ansatz of Jeziorski and Monkhorst [23]... 

The simplest way to realize an exponential expansion is to employ the exponential ansdtz of Jeziorski and Monkhorst [87] which exploits a complete model space. This is the approach that we followed in Section 4.2.2.2 in developing a multi-root multireference Brillouin-Wigner coupled cluster theory. The Jeziorski and Monkhorst exponential ansatz may be written... 

If we now substitute the Hilbert space exponential ansatz of Jeziorski and Monkhorst, expression (4.103), for the wave operator, 17, then we obtain the following system of equations... 

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