Biomedical subjects

Roberto L A Haiduke

Publications and source records attributed to Roberto L A Haiduke.

7 recordsLinked to original sources

PubMed2007

QTAIM charge-charge flux-dipole flux models for the infrared fundamental intensities of difluoro- and dichloroethylenes.

A quantum theory of atoms in molecules (QTAIM) charge-charge flux-dipole flux (CCFDF) decomposition of the MP2/6-311++G(3d,3p) level molecular dipole moment derivatives is reported for the cis-, trans-, and 1,1-difluoroethylenes and the cis- and trans-dichloroethylenes. Although the dipole moment derivatives and infrared fundamental intensities calculated at the MP2 level are overestimated for high-intensity bands corresponding to CF and CC stretching vibrations, the overall agreement is good with a root-mean-square (rms) error of 19.6 km mol-1 for intensities ranging from 0 to 217.7 km mol-1. The intensities calculated from the QTAIM/CCFDF model parameters are in excellent agreement with those calculated directly by the MP2/6-311++G(3d,3p) approach with only a 1.8 km mol-1 rms error. A high negative correlation (r=-0.91) is found between the charge flux and dipole flux contributions to the dipole moment derivatives. Characteristic values of charge, charge flux, and dipole flux contributions are found for CF, CCl, and CH stretching derivatives. The CH stretching derivatives provide especially interesting results with very high charge flux and dipole flux contributions with opposite signs. The charge, charge flux, and dipole flux contributions are found to be transferable from the cis to the trans isomers providing accurate predictions of the theoretical trans intensities with rms errors of 8.6 km mol-1 for trans-difluoroethylene and 5.9 km mol-1 for trans-dichloroethylene.

Journal Article↗

PubMed2006

The nuclear electric quadrupole moment of antimony from the molecular method.

Relativistic Dirac-Coulomb (DC) Hartree-Fock calculations are employed to obtain the analytic electric field gradient (EFG) on the antimony nucleus in the SbN, SbP, SbF, and SbCl molecules. The electronic correlation contribution to the EFGs is included with the DC-CCSD(T) and DC-CCSD-T approaches, also in the four-component framework, using a finite-difference method. The total EFG results, along with the experimental nuclear quadrupole coupling constants from microwave spectroscopy, allow to derive the nuclear quadrupole moments of (121)Sb and (123)Sb, respectively, as -543(11) and -692(14) mb.

Journal Article↗

PubMed2006

QTAIM charge-charge flux-dipole flux models for the infrared fundamental intensities of the fluorochloromethanes.

The molecular dipole moments, their derivatives, and the fundamental IR intensities of the fluoro-, chloro-, and fluorochloromethanes are determined from QTAIM atomic charges and dipoles and their fluxes at the MP2/6-311++G(3d,3p) level. Root-mean-square (rms) errors of 0.01 D and 5.6 km mol(-1) are found for the dipole moments and fundamental IR intensities calculated using QTAIM parameters when compared with those obtained directly from the MP2/6-311++(3d,3p) calculations and 0.04 D and 23.1 km mol(-1) when compared with the experimental values. Charge, charge flux, and dipole flux contributions are calculated for all the normal vibrations of these molecules. A large negative correlation coefficient of -0.92 is calculated between the charge flux and dipole flux contributions and indicates that electron transfer from one side of the molecule to the other during vibrations is accompanied by relaxation with electron density polarization in the opposite direction. The CF, CCl, and CH stretching normal modes of these molecules are shown to have characteristic sets of charge, charge flux, and dipole flux contributions. Although the FCF and ClCCl deformation normal modes can also be discriminated from one another based on the sizes and signs of these contributions, some HCH deformations have contributions that are similar to those for some of the ClCCl deformations.

Journal Article↗

PubMed2006

Accurate relativistic adapted Gaussian basis sets for Cesium through Radon without variational prolapse and to be used with both uniform sphere and Gaussian nucleus models.

Accurate relativistic adapted Gaussian basis sets (RAGBSs) from Cs (Z = 55) through Rn (Z = 86) without variational prolapse were developed by using the polynomial version of the Generator Coordinate Dirac-Fock method. The RAGBSs presented here can be used with any of two popular finite nucleus models, the uniform sphere and the Gaussian models. The largest RAGBS error is 4.5 mHartree for Radon with a size of 30s27p17d11f.

Cesium↗

PubMed2005

An accurate relativistic universal Gaussian basis set for hydrogen through Nobelium without variational prolapse and to be used with both uniform sphere and Gaussian nucleus models.

An accurate relativistic universal Gaussian basis set (RUGBS) from H through No without variational prolapse has been developed by employing the Generator Coordinate Dirac-Fock (GCDF) method. The behavior of our RUGBS was tested with two nuclear models: (1) the finite nucleus of uniform proton-charge distribution, and (2) the finite nucleus with a Gaussian proton-charge distribution. The largest error between our Dirac-Fock-Coulomb total energy values and those calculated numerically is 8.8 mHartree for the No atom.

Journal Article↗

PubMed2005

An atomic charge-charge flux-dipole flux atom-in-molecule decomposition for molecular dipole-moment derivatives and infrared fundamental intensities.

The molecular dipole moment and its derivatives are determined from atomic charges, atomic dipoles, and their fluxes obtained from AIM formalism and calculated at the MP2(FC)/6-311++G(3d,3p) level for 16 molecules: 6 diatomic hydrides, CO, HCN, OCS, CO2, CS2, C2H2, C2N2, H2O, H2CO, and CH4. Root-mean-square (rms) errors of 0.052 D and 0.019 e are found for the dipole moments and their derivatives calculated using AIM parameters when compared with those obtained directly from the MP2(FC)/6-311++G(3d,3p) calculations and 0.097 D and 0.049 e when compared to the experimental values. The major deviations occur for the NaH, HF, and H2O molecules. Parallel polar tensor elements for the diatomic and linear polyatomic molecules, except H2, HF, LiH, and NaH, have values resulting from cancellations of substantial contributions from atomic charge fluxes and atomic dipole fluxes. These fluxes have a large negative correlation coefficient, -0.97. IR fundamental intensity sums for CO, HCN, OCS, CO2, CS2, C2H2, C2N2, H2CO, and CH4 calculated using AIM charges, charge fluxes, and atomic dipole fluxes have rms errors of 14.9 km mol(-1) when compared with sums calculated directly from the molecular wave function and 36.2 km mol(-1) relative to experimental values. The classical model proposed here to calculate dipole-moment derivatives is compared with the charge-charge flux-overlap model long used by spectroscopists for interpreting IR vibrational intensities. The utility of the AIM atomic charges and dipoles was illustrated by calculating the forces exerted on molecules by a charged particle. AIM quantities were able to reproduce forces due to a +0.1 e particle over a 3-8-A separation range for the CO and HF molecules in collinear and perpendicular arrangements. These results show that IR intensities do contain information relevant to the study of intermolecular interactions.

Journal Article↗

PubMed2004

A polynomial version of the generator coordinate Dirac-Fock method.

A polynomial version of the Generator Coordinate Dirac-Fock (p-GCDF) method is introduced and applied to develop Adapted Gaussian Basis Sets (AGBS) for helium- and beryllium-like atomic species (He, Ne +8, Ar +16, Sn +48, Be, Ne +6, Ar +14, and Sn +46) and for Kr and Xe atoms. The Dirac-Fock-Coulomb and Dirac-Fock-Breit energies obtained with these basis sets are in excellent agreement with numerical finite-difference calculations. Moreover, the sizes of the AGBS generated here with the p-GCDF method are significantly smaller than the size of previous relativistic Gaussian basis sets.

Journal Article↗