State-specific multi-reference

Computation of Excited State Potential Energy Surfaces via Linear Response Theories Based on State Specific Multi-Reference Coupled Electron-Pair Approximation Like Methods (S. Chattopadhyay, D. Pahari, U. Mahapatra D. Mukherjee)... 

U.S. Mahapatra, S. Chattopadhyay, R.K. Chaudhuri, Second-order state-specific multi-reference Mller-Plesset perturbation theory Application to energy surfaces of diimide, ethylene, butadiene and cyclobutadiene, J. Comput. Chem. 32 (2011) 325. 

U.S. Mahapatra, B. Datta, D. Mukherjee, A state-specific multi-reference coupled cluster formalism with molecular applications. Mol. Phys. 94 (1998) 157. 

Size-consistent state-specific multi-reference methods a survey of some recent developments ... 

Size-consistent state-specific multi-reference methods... 

EMERGENCE OE STATE-SPECIFIC MULTI-REFERENCE PERTURBATION THEORY SS-MRPT FROM SS-MRCC THEORY... 

Although the approach described above is presented in its most general form, using a multiple coupled-cluster Ansatz for the SS-MRCC formalism, suitable approxi-mants to it such as the state-specific multi-reference perturbation theory (SS-MRPT) or state-specific multi-reference CEPA (SS-MRCEPA) can be generated by straightforward approximations. Since the new closed component of the wave operator for IMS appear first at the quadratic power, it is evident that the expressions we have derived in this and the earlier papers for the CAS will remain valid if the quadratic powers of are ignored in the approximants to SS-MRCC for IMS. This implies that all the SS-MRPT... 

Chapter 22 - Size-consistent state-specific multi-reference methods A survey of some recent developments, Pages 581-633, Dola Pahari, Sudip Chattopadhyay, Sanghamitra Das, Debashis Mukherjee and Uttam Sinha Mahapatra... 

In Section 4.2.3.1, we have defined the wave operator, 12, in the Brillouin-Wigner form (4.92). If we adopt an exponential ansatz for the wave operator, 12, we can develop the single-root (state-specific) multi-reference Brillouin-Wigner coupled-cluster (MR Bwcc) theory. This is the purpose of the present section. 

In Brillouin-Wigner coupled cluster theory, the simple a posteriori correction described above is exact in the case of the single-reference formalism. In the state-specific multi-reference Brillouin-Wigner coupled cluster theory, the simple a posteriori correction is approximate. An iterative correction for lack of extensivity has been studied by Kttner [38], but this reintroduces the intruder state problem. 

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