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Bauschlicher, Charles W.

Publications and source records attributed to Bauschlicher, Charles W..

28 records · Page 2
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NASA NTRS1998

Infrared Spectra of Polycyclic Aromatic Hydrocarbons: Nitrogen Substitution

The B3LYP/4-31G approach is used to compute the harmonic frequencies of substituted naphthalene, anthracene, and their cations. The substitutions include cyano (CN), aminio (NH2), imino (NH), and replacement of a CH group by a nitrogen atom. All unique sites are considered, namely 1 and 2 for naphthalene and 1, 2, and 9 for an'tracene, except for the imino, where only 2-iminonaphthalene is studied. The IR spectra of these substituted species are compared with those of the unsubstituted molecules. The addition of a CN group does not significantly affect the spectra except to add the CN stretching frequency. Replacing a CH group by N has only a small effect on the IR spectra. The addition of the NH2 group dramatically affects the neutral spectra, giving it much of the character of the cation spectra. However, the neutral 2-irrinonaphthalene spectra looks more like that of naphthalene than like the 2-aminonaphthalene spectra.

Bauschlicher, Charles W.↗
NASA NTRS1997

Quantum Chemical Calculations

The current methods of quantum chemical calculations will be reviewed. The accent will be on the accuracy that can be achieved with these methods. The basis set requirements and computer resources for the various methods will be discussed. The utility of the methods will be illustrated with some examples, which include the calculation of accurate bond energies for SiF$_n$ and SiF$_n^+$ and the modeling of chemical data storage.

Bauschlicher, Charles W.↗
NASA NTRS1997

Comparison of DFT with Traditional Methods for the Calculation of Vibrational Frequencies and Bond Energies

The vibrational frequencies of MO2 are computed at many levels of theory, including HF, B3LYP, BP86, CASSCF, MP2, and CCSD(T). The computed results are compared with the available experimental results. Most of the methods fail for at least one state of the systems considered. The accuracy of the results and the origin of the observed failures are discussed. The B3LYP bond energies are compared with traditional methods for a variety of systems, ranging from FeCOn+ to SiCln and its positive ions. The cases where B3LYP differs from the traditional methods are discussed.

Bauschlicher, Charles W.↗
NASA NTRS1997

The Calculation of Accurate Metal-Ligand Bond Energies

The optimization of the geometry and calculation of zero-point energies are carried out at the B3LYP level of theory. The bond energies are determined at this level, as well as at the CCSD(T) level using very large basis sets. The successive OH bond energies to the first row transition metal cations are reported. For most systems there has been an experimental determination of the first OH. In general, the CCSD(T) values are in good agreement with experiment. The bonding changes from mostly covalent for the early metals to mostly electrostatic for the late transition metal systems.

Bauschlicher, Charles W.↗
NASA NTRS1997

Differentiating Between H and F or H and CN on C(III) or Si(III) Surfaces

A Sc tipped probe molecule yields a larger difference for the probe-H vs probe-F interaction energies than our previously studied, electron-rich pyridine (C5H5N) and (CH3)3PO probes. However, the electron-deficient Sc tipped probe does not eliminate the probe-nearest data neighbor interaction problem associated with the C(III) surface. The difference in the probe-H and probe-F interaction energies is smaller for Si(III) than C(III), making it more difficult to differentiate between these two atoms on Si(III). The larger lattice constant for Si(III) significantly reduces the data atom-data atom interaction energy as well as the probe-neighbor interaction energies. This means that the H/CN system which is not practical for C(III) due to the CN-CN repulsion, is possible for Si(III). The difference in the probe-H and probe-CN interaction energies is very large for the H/CN data storage system, making this the best system studied to date. This system could be used on C(III) if a hydrogen 'fence' is built around each data site, which corresponds to using only one quarter of the surface sites for data storage.

Bauschlicher, Charles W.↗
NASA NTRS1996

The Application B3LYP to Large Systems

The application of density functional theory (DFT), using the B3LYP functional, to a series of chemical problems is described. The first involves the calculation of silica-adsorbate bond energies, including both chemical bonds and weak hydrogen bonding. The calculation of vibrational frequencies for large organic systems is discussed. For the closed shell neutral systems, the B3LYP results are similar to the self- consistent- field results, however, for the positive ions, only the B3LYP level of theory is accurate and sufficiently inexpensive to allow the study of large systems. The final application involves the calculation of successive metal-ligand bond energies. The B3LYP bond energies and entropies are shown to be in good agreement with experiment.

Bauschlicher, Charles W.↗
NASA NTRS1994

A Comparison of Density Functional Theory with Ab initio Approaches for Systems Involving First Transition Row Metals

Density functional theory (DFT) is found to give a better description of the geometries and vibrational frequencies of FeL and FeL(sup +) systems than second order Moller Plesset perturbation theory (MP2). Namely, the DFT correctly predicts the shift in the CO vibrational frequency between free CO and the Sigma(sup -) state of FeCO and yields a good result for the Fe-C distance in the quartet states of FeCH4(+) 4 These are properties where the MP2 results are unsatisfactory. Thus DFT appears to be an excellent approach for optimizing the geometries and computing the zero-point energies of systems containing first transition row atoms. Because the DFT approach is biased in favor of the 3d(exp 7) occupation, whereas the more traditional approaches are biased in favor of the 3d(exp 6) occupation, differences are found in the relative ordering of states. It is shown that if the dissociation is computed to the most appropriate atomic asymptote and corrected to the ground state asymptote using the experimental separations, the DFT results are in good agreement with high levels of theory. The energetics at the DFT level are much superior to the MP2 and in most cases in good agreement with high levels of theory.

Ricca, Alessandra↗
NASA NTRS1989

The permanent electric dipole moment of chromium monoxide

The permanent electric dipole moments for the X 5Pi and B 5pi states of gas-phase CrO have been experimentally determined using the sub-Doppler optical technique of intermodulated fluorescence spectroscopy in conjunction with the Stark effect. The measured values are 3.88 + or - 0.13 and 4.1 + or - 1.8 D for the X and B states, respectively. The theoretical values determined for the X state using multireference CI iterative-natural-orbital and finite-field calculations are in excellent agreement with the experimental value.

Steimle, Timothy C.↗
NASA NTRS1987

Theoretical approaches to metal chemistry

Theoretical calculations on metals ranging from very accurate ab initio studies of diatomic and triatomic systems to model studies of larger clusters are presented. Recent improvements in the representation of one-particle and n-particle spaces have made possible the prediction that Al2 has a 3Pi(u) ground state, even though the 3Sigma(-)g state lies within 200/cm. Results suggest that cluster geometry varies dramatically with cluster size, and that rather large clusters are required before the bulk structure becomes optimal. Al cluster studies show that three-body terms are needed for quantitative agreement with ab initio calculations.

Bauschlicher, Charles W.↗