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We present an N5scaling modification to the standard EOMEA-CCSD method, based on the matrix partitioning technique and perturbative approximations. The method has lower computational scaling and smaller storage requirements than the standard EOMEA-CCSD method and, therefore, can be used to calculate electron affinities of large molecules and clusters. The performance and capabilities of the new method have been benchmarked with the standard EOMEA-CCSD method, for a test set of 20 small molecules, and the average absolute deviation is only 0.03 eV. The method is further used to investigate electron affinities of DNA and RNA nucleobases, and the results are in excellent agreement with the experimental values.

We report a theoretical investigation on the NOxcatalyzed pathways of stratospheric ozone depletion using highly accurate coupled cluster methods. These catalytic reactions represent a great challenge to state-of-the-art ab initiomethods, while their mechanisms remain unclear to both experimentalists and theoreticians. In this work, we have used the so-called “gold standard of quantum chemistry,” the CCSD(T) method, to identify the saddle points on NOx-based reaction pathways of ozone hole formation. Energies of the saddle points are calculated using the multireference variants of coupled cluster methods. The calculated activation energies and rate constants show good agreement with available experimental results. Tropospheric precursors to stratospheric NOxradicals have been identified, and their potential importance in stratospheric chemistry has been discussed. Our calculations resolve previous conflicts between ab initioand experimental results for a trans nitro peroxide intermediate, in the NOxcatalyzed pathway of ozone depletion.

We report the static dipole polarizability and first-hyperpolarizability of the sodium atom clusters, Nan, n2, 4, 6 and 8, using our recent implementation of a numerical-analytical approach to the coupled-perturbed Kohn−Sham (CPKS) equations in deMon2k. The calculations are reported for VWN and BP86 exchange-correlation functionals using Sadlej and TZVP-FIP1 basis sets which have been previously optimized for polarizability calculations. All-electron calculations were performed for the optimizations at the VWN/DZVP/A2 and PW86/DZVP/A2 levels. Comparisons are made with Hartree−Fock (HF) and MP2 benchmark calculations.