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MRCC is a package of ab initio and density functional quantum chemistry programs for accurate electronic structure calculations. The suite has efficient implementations of both low- and high-level correlation methods, such as second-order Møller-Plesset (MP2), random-phase approximation (RPA), second-order algebraic-diagrammatic construction [ADC(2)], coupled-cluster (CC), configuration interaction (CI), and related techniques. It has a state-of-the-art CC singles and doubles with perturbative triples [CCSD(T)] code, and its specialties, the arbitrary-order iterative and perturbative CC methods developed by automated programming tools, enable achieving convergence with regard to the level of correlation. The package also offers a collection of multi-reference CC and CI approaches. Efficient implementations of density functional theory (DFT) and more advanced combined DFT-wave function approaches are also available. Its other special features, the highly competitive linear-scaling local correlation schemes, allow for MP2, RPA, ADC(2), CCSD(T), and higher-order CC calculations for extended systems. Local correlation calculations can be considerably accelerated by multi-level approximations and DFT-embedding techniques, and an interface to molecular dynamics software is provided for quantum mechanics/molecular mechanics calculations. All components of MRCC support shared-memory parallelism, and multi-node parallelization is also available for various methods. For academic purposes, the package is available free of charge.

The size limit of substituents allowingO-through-the-annulus rotation of substituted calix[4]arenes was further extended to the propargyloxy group in 24-propargyloxy-25,26,27-tris(N,N-dimethylcarbamoylmethoxy)-p-tert-butylcalix[4]arene by demonstrating its free but slow motion affording equilibrium between the partial cone and 1,2-alternate conformers. The effect of solvent and upper rim substituents R1on the conformational inversion was investigated by means of1H NMR. The rotational isomerisation of the parent (R1= H) analogue could not unambiguously be detected. The experimental results were supported by comprehensive density functional theory studies. [ABSTRACT FROM AUTHOR]

• O 2 adsorption on the defected surface is favored compared to the pure surface. • At higher potentials, the oxygen reduction reaction goes through the formation of HO 2. • At lower potentials, the formation of a small amount of H 2 O 2 is also expected. • The rate-limiting step is the final reduction of the adsorbed OH to form H 2 O. The goal of this study is to provide insight into the mechanism of the oxygen reduction reaction on the TiO 2 rutile (1 1 0) surface in the presence of bridging hydroxyl groups. Considering the Langmuir–Hinshelwood and Eley–Rideal mechanisms, each possible intermediate was identified using density functional theory and a cluster model along with the energy barriers of the reduction steps and the O O bond breaking. Our results show that the initial step, the O 2 adsorption on the surface, is favored compared to the pure surface. At higher potentials, the oxygen reduction reaction was found to go through the formation of HO 2 , which can easily convert to two terminal hydroxyl groups. The rate-limiting step is the desorption of the first H 2 O with 0.58 eV energy requirement at zero applied potential, while at 1.23 V the reduction of the adsorbed OH to form H 2 O is the bottleneck with a barrier height of 1.71 eV. [ABSTRACT FROM AUTHOR]