01735nas a2200145   4500008004100000022001400041245011200055210006900167260008700236300001100323490000800334520110100342100002101443856012501464       2014                        eng d  a0021-960600aPerturbative approximation to hybrid equation of motion coupled cluster/effective fragment potential method0 aPerturbative approximation to hybrid equation of motion coupled   a1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USAbAMER INST PHYSICScMAR  a0941010 v1403 a<p>Hybrid quantum mechanics/molecular mechanics (QM/MM) methods provide an attractive way to closely retain the accuracy of the QM method with the favorable computational scaling of the MM method. Therefore, it is not surprising that QM/MM methods are being increasingly used for large chemical/biological systems. Hybrid equation of motion coupled cluster singles doubles/effective fragment potential (EOM-CCSD/EFP) methods have been developed over the last few years to understand the effect of solvents and other condensed phases on the electronic spectra of chromophores. However, the computational cost of this approach is still dominated by the steep scaling of the EOM-CCSD method. In this work, we propose and implement perturbative approximations to the EOM-CCSD method in this hybrid scheme to reduce the cost of EOM-CCSD/EFP. The timings and accuracy of this hybrid approach is tested for calculation of ionization energies, excitation energies, and electron affinities of microsolvated nucleic acid bases (thymine and cytosine), phenol, and phenolate. (C) 2014 AIP Publishing LLC.</p>1 aGhosh, Debashree  uhttps://library.ncl.res.in/content/perturbative-approximation-hybrid-equation-motion-coupled-clustereffective-fragment-0