EOM-CCSD method

Table 3 Second Order Properties Calculated by EOM-CCSD Methods...

Pecul calculated the 1J(3He,3He) coupling in ,154 i.e., one of the weakest bonded van der Waals complexes, using full Cl46 and EOM-CCSD methods.44,155 158 She found that in this complex the FC term of such coupling decreases exponentially with the d(He-He) distance being He, 3He) 22 Hz, for d(He He) = 4 au and falling below 0.1 Hz for d(He-He) = 7 au. Pecul concluded that the main FC coupling pathway is the overlap between the electronic clouds of both helium atoms and that its efficiency does not depend on whether this corresponds to an attractive or repulsive interaction. Similarly, Pecul et al.159 carried out calculations based on... 

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 partitioned equation-of-motion second-order many-body perturbation theory [P-EOM-MBPT(2)] [67] is an approximation to equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) [17], which will be fully described in Section 2.4. The EOM-CCSD method diagonalizes the coupled-cluster effective Hamiltonian H = [HeTl+T2) in the singles and doubles space, i.e.,... 

The EOM-CCSD method offers an accurate treatment of states that are largely described by single excitations, and it gives a considerably poorer description of doubly excited states. For a discussion, see Ref. 190. 

Although length of the many-body expansion of Hn,open is enormous, very few terms enter a particular approximate scheme. For example, the EOM-CCSD method needs one- and two-body components of H and certain types of the three-body H3 terms [33,34] (for further comments, see Ref. 60 cf., also, Sections 4 and 5). The situation gets complicated if we want to go beyond the EOMCCSD approximation and represent T as a sum of, for example, I), T2, and T3 components. For this reason, the only higher-than-two-body terms included in the current implementation of the EOM-CCSDT scheme are the three-body terms of the EOMCCSD method [46]. This approximation seems to work very well, even though the EOMCCSDT procedure defined in this way remains an n8 method. 

The scalar spin-spin coupling has been calculated by Pecul for the helium dimer using full configuration interaction and EOM-CCSD methods. The... 

A few versions of CC theory have been developed for treating excited states. One such version, the equation-of-motion (EOM) CCSD, has given very good results for vertical excitation energies. Analytic gradients for the EOM-CCSD method are available, allowing calculation of geometries and vibrational frequencies of excited states. For details see R. J. Bartlett in Yarkony, Part II, Chapter 16, Section 9. 

Towards the accurate simulation of UVA is spectra in solution combining the EOM-CCSD method with polarizable solvation models within state-specific and linear-response formalisms (Caricato, 42, 197-214) Strong photon-molecule coupling fields for chemical reactions (Ueno and Misawa, 29, 228-255)... 

Singlet-triplet separations of di-radicals treated by the DEA/DIP-EOM-CCSD methods... 

Spin-spin coupling constants were evaluated using the equation-of-motion coupled cluster singles and doubles (EOM-CCSD) method in the Cl (configuration interac-tion)-like approximation [52, 53], with all electrons correlated. For these calculations, the Ahlrichs [54] qzp basis set was placed on and F, and the qz2p basis... 

Mata et al have determined the dynamic polarizability and Cauchy moments of liquid water by using a sequential molecular dynamics(MD)/ quantum mechanical (QM) approach. The MD simulations are based on a polarizable model of liquid water while the QM calculations on the TDDFT and EOM-CCSD methods. For the water molecule alone, the SOS/TDDFT method using the BHandHLYP functional closely reproduces the experimental value of a(ffl), provided a vibrational correction is assumed. Then, when considering one water molecule embedded in 100 water molecules represented by point charges, a(co) decreases by about 4%. This decrease is slightly reduced when the QM part contains 2 water molecules but no further effects are observed when enlarging the QM part to 3 or 4 water molecules. These molecular properties have then been employed to simulate the real and imaginary parts of the dielectric constant of liquid water. 

Two alternatives to CASPT2 have recently appeared. One is the equation-of-motion (EOM) coupled-cluster method, which has been implemented in the ACES II program of Bartlett et al." This method, which can equally well be applied to open-shell molecules, has been reviewed, as already mentioned, in Volume 5 of this series.EOM-CC has been demonstrated to give results of similar accuracy as CASPT2 for states that do not have significant doubleexcitation character. A simplified version of this method, recently developed, can be applied to molecules up to the size of porphine. Also, it has been pointed out that because analytical gradients are available, the EOM-CCSD method is an excellent method for calculations of excited state potential energy surfaces. 

Towards the accurate simulation of UV/Vis spectra in solution combining the EOM-CCSD method with polarizable solvation models within state-specific and linear-response formalisms... 

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