Equation-of-motion coupled-cluster method EOM-CC

More demanding calculations conducted by Daniel et al. using equations-of-motion coupled cluster methods (EOM-CC) provided a better description of the contribution of MLCT andMC transitions to the electronic spectrum of Cr(CO)6 [13]. These calculations confirm that the lowest-energy transition, which is responsible for the shoulder on the low-energy side of the first absorption maximum, corresponds to... 

Electric dipole polarizability, 28 Electric polarizability, 14 Electron correlation, 8, 10 Electronic virial theorem, 15 Equation of Motion coupled cluster method (EOM-CC), 38, 54 Eulero-Lagrange equation, 51... 

Koch and Jorgensen have determined coupled cluster linear and quadratic response functions. Recently, Sekino and Bartlett have introduced an equation of motion coupled cluster method (EOM-CC)" and give results for molecules NH3 and C4H6. 

In two recent publications we have tried to characterize the excited state properties of 1 and 3 in order to facilitate their detection by LIF-spectroscopy. Our main tool in this effort has been equation of motion coupled cluster theory (EOM-CC). The EOM-CCSD method, which is equivalent to linear response CCSD, has been shown to provide an accurate description of both valence and excited states even in systems where electron correlation effects play an important role [39]. Computed transition energies for excitations that are of mainly single substitution character are generally accurate to within 0.1 eV. We have found the EOM-CCSD method to perform particularly well in combination with the doubly-augmented cc-pVDZ (d-aug-cc-pVDZ) basis set. This basis seems to provide equally balanced descriptions of ground and excited states,... 

The vertical IPs of CO deserve special attention because carbon monoxide is a reference compound for the application of photoelectron spectroscopy (PES) to the study of adsorption of gases on metallic surfaces. Hence, the IP of free CO is well-known and has been very accurately measured [62]. A number of very efficient theoretical methods specially devoted to the calculation of ionization energies can be found in the literature. Most of these are related to the so-called random phase approximation (RPA) [63]. The most common formulations result in the equation-of-motion coupled-cluster (EOM-CC) equations [59] and the one-particle Green s function equations [64,65] or similar formalisms [65,66]. These are powerful ways of dealing with IP calculations because the ionization energies are directly obtained as roots of the equations, and the repolarization or relaxation of the MOs upon ionization is implicitly taken into account [59]. In the present work we remain close to the Cl procedures so that a separate calculation is required for each state of the cation and of the ground state of the neutral to obtain the IP values. 

As follows from the form of the QM/MM Hamiltonian (Eq. 5.8), any electronic structure method can be used for describing the QM and MM parts of the system. Applications discussed in the following session mainly deal with understanding photochemistry in the condensed phase, with a common choice of the excited state methods from the equation of motion coupled cluster (EOM-CC) family [61-64], time-dependent density functional theory (TD-DFT) [65-66], or configuration interaction (Cl) methods. The MM Hamiltonian is represented by either EFPl or EFP Hamiltonian from Eq. 5.1 or Eq. 5.7. //qm-mm coupling term in the QM/EFPl... 

The CC method is used to calculate the ground-state energy and wave function. What about the excited states This is a task for the equation-of-motion coupled cluster (EOM-CC) method, the primary goal being not the excited states themselves, but the excitation energies with respect to the ground state. 

The equation-of-motion coupled-cluster (EOM-CC) method is based on the CC wave function obtained for the ground state and is designed to provide the electronic excitation energies and the corresponding excited-state wave functions. 

EOM-CC Equation-of-Motion Coupled Cluster A non-variational method of solving... 

EOM-CC Equation-of-Motion Coupled Cluster A non-variational method of solving the Schrddinger equation for excited states (related to the equation of motion, EOM), with the wave function calculated in the coupled cluster (CC) method. 

Applying the time-dependent perturbation is straigthforward and leads to LR-CC methods. The nonlinear systems of equations include the normal T and Ti (for CCSD) operators-amplitudes and additionally single and double excitation (time-dependent) response amplitudes (for details the reader is referred to Refs. 1, 64, 88, 89 and references cited therein). An alternative approach, that, although conceptually different yields exactly the same excitation energies, is the equation-of-motion coupled cluster (EOM-CC) method [90]. The EOM-CC equations also contain the CC wave function 4 cc) (Eq. [50]) and a second (state-dependent) excitation operator R including single, double,. .. excitations (usually R is truncated in the same manner as T). The EOM equations read as... 

Excited states may be studied using the general post-Hartree-Fock methods listed above, or some specialized techniques, such as configmation interaction with single substitutions (CIS) (Foresman et al. 1992), time-dependent density functional theory (TDDFT) (Dreuw and Head-Cordon 2005 Elliott et al. 2009), equations-of-motion coupled cluster (EOM-CC) (Kowalski and Piecuch 2004 Wloch et al. 2005). 

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