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 H-2, 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-angstrom 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.109112680268

The infrared fundamental intensities and polar tensor of allene

The polar tenser of allene was calculated from the infrared fundamental band intensities of C,H, and C,D,. The ambiguities in the signs of the dipole moment derivatives with respect to their normal coordinates were resolved by comparison of tenser elements with ab initio calculations at the B3LYP, MP2(FC) and CCD(FC) levels with a 6/311 + + G(3d,3p) basis set. The results are similar to those previously obtained by Koga and co-workers except for the choice of an average of two sign combinations fur the E symmetry elements. The values of the mean dipole moment derivatives for the sp and sp(2) carbon atoms obtained in this work, 0.032 and -0.133 e, respectively, are in good agreement with the CCD(FC)/6-311 + + G(3d,3p), 0.061 and - 0.128 e, and MP2(FC)/6-311 + + G(3d,3p), 0.072 and -0.153 c, theoretical results. The mean dipole moment derivatives are shown to be consistent with potential models relating Is electron ionization energies and atomic charges. (C) 2001 Elsevier Science B.V. All rights reserved.5771369137

The infrared vibrational intensities and polar tensors of HFCO and DFCO

The infrared vibrational intensities of HFCO and DFCO have been calculated at the B3LYP/cc-pVTZ, MP2(FC)/6-311++G(3d,3p) and QCISD(FU)/aug-cc-pVTZ levels. All calculations predict the isotopomers to have identical intensity sums, within about 1 km mol(-1). This is in contrast with experimental intensity sum results reported in the literature. Dipole moment derivative directions calculated by the three methods are in excellent agreement for all in-plane normal coordinates. All the theoretical polar tensor elements are also in good agreement with each other having standard deviations varying between 0.003 and 0.043 e. The oxygen and fluorine atoms have negative mean derivatives (approximate to-0.6 e), whereas the carbon mean derivative is very positive (approximate to+1.1 e) and the hydrogen one is almost zero (approximate to+0.03 e). The HFCO theoretical intensity sums calculated by all three methods as well as their carbon and oxygen mean dipole moment derivatives are in good agreement with those estimated from the experimental intensities and atomic mean derivatives of H2CO and F2CO. (C) 2003 Elsevier B.V. All rights reserved.60132947295

The infrared fundamental intensities and polar tensor of CH3NC

The molecular force field and polar tensor of methyl isocyanide have been determined from its gas phase vibrational frequencies and infrared intensities. Quantum chemical results from MP2(FC), B3LYP and quadratic configuration interaction calculation including single and double substitutions procedures using a 6-311 + +G(3d,3p) basis set have been used to determine the signs of the dipole moment derivatives with respect to the normal coordinates as well as estimate individual fundamental intensities of the overlapped upsilon(1)-upsilon(5) and upsilon(3)-upsilon(6) band systems. Principal component graphical representations of the A, and E symmetry polar tensor elements were useful in determining preferred sets of tensor elements. The mean dipole moment derivative (GAPT charge) of the methyl carbon in CH3NC, 0.347 e, is between the corresponding values in CH3CN, 0.110 e, and CH3F, 0.541 e. The mean dipole moment derivatives obtained here indicate the correct Is methyl carbon ionization energy as 293.35 eV which is 0.98 eV higher than the corresponding ionization energy of the terminal atom. (C) 2002 Elsevier Science B.V. All rights reserved.591374

The infrared fundamental intensities and polar tensor of CF4

Atomic polar tensors of carbon tetrafluoride are calculated from experimental fundamental infrared intensities measured by several research groups. Quantum chemical calculations using a 6-311 + + G(3d, 3p) basis set at the Hartree-Fock, Moller-Plesset 2 and Density Functional Theory (B3LYP) levels are used to resolve the sign ambiguities of the dipole moment derivatives. The resulting carbon mean dipole moment derivative, (p) over bar(C) = 2.051 e, is in excellent agreement with values estimated by a MP2/6-311 + + G(3d, 3p) theoretical calculation, 2.040 e, and by an empirical electronegativity model. 2.016 e. The (p) over bar(C) value determined here is also in excellent agreement with the one obtained from the CF4 Is carbon ionization energy using a simple potential model, 2.059 e. Crawford's G intensity sum rule applied to the fundamental intensities of CH4, CH3F, CH2F2 and CHF3 results in a prediction of a 1249 km mol(-1) intensity sum for CF4 in good agreement with the experimental values of 1328 +/- 37.9, 1208.0 +/- 54.4 and 1194.8 +/- 7.4 km mol(-1) reported in the literature. (C) 2000 Elsevier Science B.V. All rights reserved.5671329133

Atomic mean dipole moment derivative and anisotropic contributions to molecular infrared intensity sums

Atomic anisotropies determined from gas-phase infrared fundamental intensity data for 30 molecules are compared with anisotropies calculated from wave functions obtained with 6-31 +G(d,p) and 6-311 ++G(3d,3p) basis sets at the Hartree-Fock, B3LYP density functional and MP2 electron correlation levels. The discrepancies between the experimental and theoretical anisotropy values are up to 30 times larger than those found for the mean dipole moment derivatives. Although a change in the basis set from 6-31+G(d,p) to 6-311++G(3d,3p) has small effects on the anisotropy values, they are quite sensitive to the inclusion of post-Hartree-Fock electron correlation treatment. Although the calculated results for anisotropies with values <0.7e(2) deviate randomly from the experimental results, calculated anisotropies with higher values tend to overestimate the experimental values. Molecules with double bonds (CH2CF2, COH2, COF2, COCl2, cis-C2H2O2, CO2, CS2, and OCS) are found to have high atomic anisotropies and large anisotropic contributions to the experimental intensity sums, whereas these contributions are much smaller for molecules containing triple bonds. Mean dipole moment derivative contributions are predominant over anisotropic ones for the fluorochloromethanes and fluorine-rich fluoromethanes. These results are interpreted using an atoms-in-molecules charge/charge flux/dipole flux decomposition of the dipole moment derivatives of CO, CO2, CS2, OCS, HCN, C2H2, and C2N2. Large positive weighted charge flux and dipole flux contributions are canceled to a large extent by large negative weighted charge flux-dipole flux interaction terms for all these molecules. Whereas this cancellation is only partial for the double-bonded molecules, it is almost perfect for the triple-bonded ones.108326788679

Simple potential models for carbon 1s ionization energies using infrared mean dipole moment derivatives

Simple potential model relations for experimental carbon Is ionization energies (E(C,1s)) and carbon mean dipole moment derivatives ((p) over bar(C)) obtained from experimentally measured infrared fundamental band intensities are investigated for a diverse group of 29 molecules. Positive and negative correlations of the E(C,1s) values and neighboring atom electrostatic potential contributions, V, with the (p) over bar(C) values result in large variances for the E(C,1s)-V values and excellent potential model fits. MP2/6-311+ +G(3d,3p) level Koopmans' energies are shown to provide the most precise potential model fits with correlation coefficients of 0.9996, 0.9962 and 0.9960 for sp(3), sp(2) and sp hybridized carbon atoms, respectively. Potential models using experimental ionization energies adjusted by HF/6-31G(d,p) level relaxation energies are almost as precise. The slopes of the potential lines obtained using Koopmans' energies or experimental ionization energies adjusted by relaxation energies increase with increasing values of the inverse covalent sp(3), sp(2) and sp radii. Relative electrostatic potentials at carbon nuclei calculated directly from electronic densities of MP2/6-311+ +G(3d,3p) molecular orbital wave functions are shown to be in good agreement with those estimated by mean dipole moment derivatives calculated from the same wave functions. (C) 2000 Elsevier Science B.V. All rights reserved.107321121

Core ionization energies, mean dipole moment derivatives, and simple potential models for B, N, O, F, P, Cl, and Br atoms in molecules

Simple potential models relating experimental 1s electron ionization energies for B, N (sp and sp(3) hybrids), O, and F atoms; 1s and 2p ionization energies for P atoms; and 2s and 2p ionization energies for Cl atoms as a function of their atomic mean dipole moment derivatives determined from experimental gas phase infrared fundamental band intensities a-re reported. Potential models using theoretical Koopmans' energies and generalized atomic polar tensor (GAPT) charges are found to form even more precise models than those using experimental data. This is expected because the potential models depend only on the electronic structures of molecules before ionization takes place and do not take into account relaxation effects. If the experimental ionization energies are adjusted by their relaxation energies, models similar to those obtained using Koopmans' energies are determined, The models permit a simple understanding of substituent effects on core ionization energies in terms of atomic charges in molecules. Most of the potential model slopes investigated are shown to be approximately proportional to the inverse atomic radii of the atom being ionized. Core-valence electron repulsion values inferred from the potential models obtained from experimental data are somewhat smaller than those calculated using Slater orbitals of isolated atoms. The potential model intercepts for Is and 2p electrons are shown to be proportional to the square of the nuclear charge, consistent with their interpretation as core electron ionization energies of neutral atoms. 1s He, Ne, and Ar and 2p Ar, Kr, and Xe core ionization energies obey the linear relationships obtained for the model intercepts. The results suggest that mean dipole moment derivatives obtained from infrared intensities can be interpreted as atomic charges.10691824183

A simple potential model criterion for the quality of atomic charges

The simple potential model has been shown to be useful in relating core electron binding energies measured in the X-ray region with mean dipole moment derivatives obtained from experimental infrared vibrational intensities. The importance of including relaxation corrections to the experimental Is ionization energies of sp, sp(2), and sp(3) hybridized carbon atoms are investigated here. Although relaxation energies obtained from 6-31G(d,p) and 6-311++G(3df,3p) basis sets using Delta SCF calculations show differences of about 1 eV for most molecules studied, relative differences are of the order of 0.1 eV. Exceptions are the CO, CO2, COS, and CS2 molecules where discrepancies are larger. Relaxation energy corrections improve simple potential model fits with mean dipole moment derivatives for all carbon atom models but is most pronounced for the sp hybridized atoms. The simple potential model corrected for relaxation energies is investigated as a criterion for testing the quality of Mulliken, CHELPG, Bader and GAPT carbon atomic charges calculated from MP2/6-311++G(3d,3p) wave functions. The GAPT charges are in excellent agreement with the experimental mean dipole moment derivatives (within 0.067e) and provide superior statistical fits to the simple potential model when compared with those obtained for the ether charges.103254918492

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.111351552