### Main research and teaching activities

**Research activity** of the team and its PhD students is oriented to the development of quantum chemistry methods for accurate calculations of molecular properties. We paid particular attention to accurate calculations of nonlinear electric properties, chemical reactivity, intermolecular interactions, ionization potentials and electron affinities, chemistry of the atmosphere, etc. including calculations of properties of radicals and molecules in excited states. Important area of interest concerns relativistic effects on molecular properties.

**Substattial effort** is focused on further development of methods for efficient treatment of the electron correlation problem with high and controlled accuracy. Members of the team have contributed to the development of Coupled Cluster (CC) methods, particularly to the CCSD(T) method, which is occasionally called the “golden standard” of quantum chemistry, and to different variants of approximate and full iterative CCSDT method. Along with the development of highly accurate ab-initio approaches, more pragmatic methods of molecular modeling of larger systems, up to modeling of multi-molecular systems based on the principles of statistical mechanics have been the area of interest of the group.

**Recently implemented CCSD(T) method** utilizes the reduced optimized virtual orbital space (OVOS). We obtained most results using the functional that optimizes the overlap between the first-order correlated wave function in the full virtual space and the reduced space, respectively. Truncating the virtual space to, say, one halve of the original full space, the computer time for CCSD(T) calculation can be reduced by order of magnitude. We have demonstrated the potential of the method in calculations of a series of molecular properties, reaction energies, intermolecular interactions, etc. Our CCSD(T) computer programs utilize parallelism as well as Choleski decomposition, which allow efficient treatment of four index integrals and amplitudes.

**Particularly interesting ** are new developments of the explicitly correlated R12 CC theories. Calculations have so far been limited to small, few-atomic molecules; the present effort is focused to extension of their applicability to larger systems of chemical interest. This will be accomplished by introducing the auxiliary basis in approximation of the resolution of identity in evaluation of pertinent r12 –dependent integrals. Also planned is extending the theory for excited states and analytic calculation of various molecular properties.

**Research team** involves four full professors (Ivan Černušák, Vladimír Kellö, Jozef Noga and Miroslav Urban,) and associate professor (Pavel Neogrády). Five up to eight graduate students/postdocs usually participate on scientific projects.