Projects
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Zero-field splittingSpin degenerate states like triplets, quartets, quintets or higher spin multiplets are in fact never strictly degenerate. Even in molecules composed of elements like boron, carbon or nitrogen the individual sublevels split by some 0.1 to 1 cm-1. There are basicaly two main mechanisms which account for the splitting of nonrelativistic spin degenerate states of molecules in the absence of an external magnetic field: spin-spin coupling and spin-orbit coupling. Since 2003 we have been developing a computer program (sometimes dubbed SOSS) for various pseudo-relativistic calculations with several 2-component Hamiltonians. The program requires a set of nonrelativistic (state specific or state averaged) CASSCF wave functions of all the relevant spin multiplicities and calculates the corresponding set of pseudo-relativistic wave functions and energies by means of quasi-degenerate perturbation theory. The program uses either the full Breit-Pauli spin-orbit Hamiltonian, or the full/mean-field DKH1 spin-orbit Hamiltonian and/or the Breit-Pauli spin-spin Hamiltonian. Zero-field splittings of spin degenerate states may conveniently be obtained from the calculated pseudo-relativistic energies. The calculated pseudo-relativistic wave functions may be used for the evaluation of radiative spin-forbidden transition probabilities, or, if the molecule is chiral, for the evaluation of the expectation value of the 2-component parity violation Hamiltonian. |
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Theoretical prediction of pKaThe COSMO-RS method is used for the prediction of base pKa contants. This method is a combination of the quantum chemical dielectric continuum solvation model COSMO with a statistical thermodynamics treatment for realistic solvation simulations. The values of the free energies of dissociation in water showed a very good correlation with experimental values of pKa. The pKa values have been calculated for a 12 synthesized amino- and (amino) guanidinopurine nucleotide, such as acyclic nucleoside phosphonate, acyclic nucleoside phosphonate diesters and other related compounds. These compounds bear characteristic pharmacophores contained in various important biologically active substances, such as cytostatics and antivirals. |
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Photophysics and PhotochemistryStudying of excited states of molecules is of considerable interest for both theoreticians and experimentalists. Theory can provide usefull informations, which are usually not accessible from experiment: character of the electronic transition, symmetry of the states involved in studied process, mechanism of photochemical reaction etc. Because even electronic ground states of many molecules can not be treated correctly with single-determinant methods, we use multireference methods like CASSCF, CASPT2, MRCI. We study either photophysical processes (interpretation of UV-VIS spectra of mainly organic molecules, description of low-lying states of different multiplicity of transition metal complexes), or photochemical processes (description of mechanisms of photochemical reactions, often including spin-forbidden transitions). |