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National Repository of Grey Literature 2 records found  Search took 0.00 seconds. 
Quantum mechanical study of the electron hopingp rocesses of heterocyclic molecules.Simulation of absorption and emission spectra.
 Tichý, Ondřej ; Burda, Jaroslav (advisor) ; Profant, Václav (referee)
This thesis is about computing lifetimes of excited states of molecules by using semiempirical methods in simulations of molecular dynamics. Pyrimidine nucleobases and three aza- derivatives were chosen as reference molecules. Simulations of molecular dynamics by program MNDO99 were performed with these molecules and static spectra were computed by programs Gaussian and Orca. All the examined molecules have femtosecond lifetimes of second excited states, pyrimidine nucleobases have also short lifetimes of first excited states in hundreds of femtoseconds. The computed first excited states of aza-derivatives have lifetimes in tens or hundreds of picoseconds and suggest that the higher stability of the states is related to the smaller number of amino groups attached to the ring.
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Použitelnost výpočetních metod kvantové chemie pro studium interakcí v biologických systémech
 PLAČKOVÁ, Lydie
The theoretical part of the Master´s thesis describes ab initio methods in quantum chemistry and semiempirical methods, which represents a way in overcoming of main disadvantages in ab initio methods (costs, speed). The experimental part was focused on comparison highly accurate CCSD(T) method with used semiempirical methods (AM1, PM3, PM6, and PM7). The data were mostly compared on small model systems with ions, which are an essential part of many biological systems. Furthermore, the applicability of semiempirical methods was examined for the description of intra- and intermolecular hydrogen bonds and van der Waals interactions.
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