Bases gaussianas geradas em ambientes atômico e molecular
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2014-09-19
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Arruda, Priscilla Mendes
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Universidade Federal do Espírito Santo
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A Gaussian basis set of small size for the atoms from H through Ar was constructed from a single sequence of exponents of 19 Gaussian functions, based on the generator coordinate Hartree-Fock method. For each atom studied a segmented contraction scheme was proposed and polarization functions and di use functions were added. Applications of the new contracted and uncontracted basis sets for the the calculation of the equilibrium geometries and electric properties (electric dipole moments and polarizabilities) of various molecular systems were performed and comparisons were made between theoretical and experimental results. The universal Gaussian basis sets presented in this work (with and without contraction) are competitive when compared to adapted basis sets of similar size. The Monte Carlo simulated annealing method was adapted to optimize correlated Gaussian-type functions in non-relativistic molecular environments. Starting from an atom-centered atomic Gaussian basis set, the uncontracted functions were reoptimized in the molecular environments corresponding to the BF, CN -, CO, CO2, CS, H2O, N2 and NO+ systems. These new molecule-optimized basis sets, called hybrid-basis sets HXZP (X = D, T, Q, and 5), were used to calculate total energies, harmonic vibrational frequencies, equilibrium geometries, electric dipole moments, and polarizabilities, at correlated level of theory. The present methodology is a simple and e ective way to improve molecular correlated wave functions, without the need to enlarge the molecular basis set. This methodology was employed to generate hierarchical sequences of molecular basis sets with increasing size, which we used to obtain complete basis set limits. xv xvi Additionally, the Monte Carlo simulated annealing method was employed to generate a hierarchical sequence of molecule-optimized basis set to CN -, CO, CO2, CS, H2O, N2 and NO+ systems. In these basis sets, all exponents were optimized in the molecular environment. Contraction schemes were proposed to each studied system, resulting in a nal molecular basis set, which we called MXZP (X = D, T, and Q). We used this hierarchical sequence of basis set to calculate total energies, harmonic vibrational frequencies, equilibrium geometries, electric dipole moments, and polarizabilities, at correlated level of theory. Also, we used that hierarchical sequences of molecular basis sets to obtain complete basis set limits. We veri ed, for the studied systems, that the MXZP basis sets produced more suitable molecular properties than the corresponding HXZP basis sets
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ARRUDA, Priscilla Mendes. Bases gaussianas geradas em ambientes atômico e molecular. 2014. 153 f. Tese (Doutorado em Física) – Universidade Federal do Espírito Santo, Vitória, 2014.