Abstract: A computational study of the compound containing selenium, 2-selenobarbituric acid, has been carried out. Tautomerism has been studied not only in neutral forms but also in the protonated and deprotonated species. The most stable tautomers for neutral and deprotonated species are equivalent to those obtained by different authors for the analogous barbituric and 2-thiobarbituric acids. However, the most stable tautomer for the protonated 2-selenobarbituric acid differs of that proposed for the analogous compounds. The enthalpy of formation in the gas phase, and the gas-phase acidity and basicity of 2-selenobarbituric acid have been calculated at the G3 and G4 levels, together with the corresponding values for barbituric and 2-thiobarbituric acids. The calculated acidity shows that 2-selenobarbituric acid is a very strong Brønsted acid in the gas phase.

Abstract: Detailed DFT computations and quantum dynamics simulations have been carried out to establish the origin of the extra stability of alloxan.. The effect of solvent, basis set and DFT methods have been examined. Two non-covalent intermolecular dimers of alloxan, namely the H-bonded and the dipolar dimers have been investigated to establish their relative stability. Quantum chemical topology features and NBO analysis have been performed.

Abstract: This study investigates the importance of the p-function used in the computational modeling. The geometric changes of ReH7(PMe3)2 system is used as the model compound. 6-31G, 6-311G and 6-311++G basis sets were used for all elements except Re, which used Christiansen et. al. basis set. Upon removing the p-function on metal, we noticed the geometric changes are minimal as long as triple-zeta basis sets are used for rest of elements. While the relative energy profile of a reaction would still reasonably assemble each other, a direct comparison in energy between the basis set with and without p-function is not recommended

Abstract: The geometry, energetics and dipole moment of the most stable conformers of cytosine in the ground state were calculated at different density functional methods, namely, B3LYP, M06-2X, ωB97-D and PEBPEB methods and the 6-311++G(3df,3pd) basis set. The most stable conformer, the keto-amino conformer is only 1 Kcal/mol more stable than the imino-enol form. The ultrafast radiationless decay mechanism has been theoretically investigated using Complete Active Space Multiconfiguration SCF calculation. The conical intersection seam was searched in the full dimensional space for the vibrational degrees of freedom. A new conical intersection has been identified, a semi-planar conical intersection (SPCI) with main deformations inside the cytosine ring and C=O bond. The g-vector and h-vector for the semi-planar conical intersection were calculated and discussed along with their geometrical parameters. A classical trajectory dynamic simulation has been performed to characterize and identify the evolution of geometry and energy changes of the SPCI with time.