Extended Basis Set Calculations Research Articles

Geometry and binding energy of ClF and ClF3

Abstract Extended basis set calculations have been performed for ClF and ClF3 using the CPF method, a size consistent modification of the Cl(SD), to clarify discrepancies between experiment and previous computations. Good agreement is found for ClF for the large 3d2flg polarization basis: re = 163 pm (exp: 162.8). De = 2.45 eV (2.67). μe = 0.85 D (0.89). ΔE for the reaction 1 2 F2 + 1 2 Cl2 ⇌ ClF is already accurate on the 2dlf level: ΔE = −53.7 kJ mol−1 (−56.0). Correlation effects involving the 2s orbital of F are shown to be non-negligible. Agreement is slightly poorer for ClF3, since only the 2dlf basis could be used: reeq = 160.7 pm (159.7), reax = 171 pm (169.8). ∠FClF = 87.1° (87.3°). The computation of ΔE (ClF3 ⇌ ClF+F2) turned out to be difficult: ΔE = 59.3 kJ mol−1 (113) on the 2dlf level. Various extensions of the basis lead to improvements of a few kJ mol−1 each, the estimate for the 3d2flg basis is ΔE ⋍ 80 kJ mol−1. The remaining discrepancy to experiment is attributed to incomplete error cancellation within CPF arising from the very different binding in ClF3 (three-centre-four-electron bonding) as compared to ClF and F2.

Compact basis sets for LCAO‐LSD calculations. Part II: Tests for Cr2 and Ni4

AbstractThe compact orbital and auxiliary basis sets for LCAO‐LSD calculations introduced in Part I are tested in molecular calculations on Cr2 and Ni4. The present results for spectroscopic constants and valence orbital energies obtained using medium size orbital expansions with a double‐zeta representation for valence orbitals are in very good agreement with those previously calculated with very extended sets. Since the computational time of the present calculations is reduced severalfold compared with the extended basis set calculations, the present basis sets allow increased efficiency of the LCAO‐LSD calculations and allow the method to be extended to larger systems.

Quantum mechanical approach to IR intensities via nuclear electric shielding tensors. I. Water

The connection between the nuclear electric shielding and the atomic polar tensors are shown. The electric shielding tensors are related to the polarizability and the magnetizability, and satisfy a constraint condition for the electrostatic equilibrium which is the mixed length-acceleration Thomas–Reiche–Kuhn sum rule. In addition, they can be successfully used to rationalize experimental IR intensity data, which is verified by extended basis set calculations on the water molecule.

Electronic spectra of mono-olefins. RPA calculations on ethylene, propene, and cis- and trans-2-butene

We present ab initio extended basis set calculations on the electronic spectra of ethylene, propene, and cis- and trans-2-butene in the random-phase approximation (RPA). All computed singlet excitations correlating with ethylene states below 9.3 eV are assigned and discussed with reference to experiment with an overall agreement better than 0.2 eV. The effects of methyl substitution and diffuse basis sets are discussed, and it is shown that the quantization axes of the Rydberg p and d orbitals in the substituted olefins are not the same as those in ethylene.

Theoretical studies of lithium bonding in lithium chloride/aliphatic amine complexes

In the systematic study of amine … LiCl [amines = NH 3, CH 3NH 2, (CH 3) 2NH] complexes the possibility of an ion-pair structure and the effect of methylation on the stabilization energy is investigated. Δ Eis evaluated by the SCF/4-31G method and augmented by the approximate dispersion energy calculated perturbationally. The interaction energy decreases with the increasing number of methyl groups in the amine. The dispersion energy plays a negligible role in the stabilization of complexes. None of the systems studied are ion pairs; their Li bonds are of a so-called molecular type. Due to the divergence of the multipole expansion, the attempt to correct the 4-31G stabilization energies via the electrostatic energy fails. The relative order of the Δ E in the series of complexes is verified instead in the extended basis set calculation. The lithium bonds are compared with their H-bonded analogues.

Electronic structure and bonding in the ground state of Cu 2

Extended basis set calculations have been performed for the ground state of Cu 2 using CI(SD) and the coupled pair functional (CPF) method, a size-consistent modification of CI(SD). Special emphasis is given to the discussion of (i) basis saturation effects (up to g functions were included), (ii) effects of cluster corrections to achieve size consistency, (iii) relativistic effects, which were included in first order from the Cowan-Griffin operator. The final results are R e = 4.23 au = 2.238 A, D e = 1.84 eV, in close agreement with experimental values of 4.20 au = 2.22 A and 2.05 eV, respectively.

The Dirac equation in the algebraic approximation. II. Extended basis set calculations for hydrogenic atoms

For pt.I see ibid., vol.17, p.L45 (1984b). The solution of the Dirac equation for hydrogen-like atoms within the algebraic approximation, that is, by using a finite basis set, is considered. It is shown that by making an appropriate choice of basis functions the problem which has been termed 'variational collapse' can be avoided. Applications using a systematic sequence of even-tempered basis sets are presented and convergence of the calculated energies within the algebraic approximation to the exact energies with increasing size of basis set is investigated.

Diatomics-in-molecules potential energy surfaces of (HeH2)+: An extended basis set calculation

Abstract Within the framework of the non-hermitean DIM formulation of Tully and Truesdale, and using 13 symmetry-adapted polyatomic basis functions, ground-state and excited-state potential energy surfaces for (HeH 2 ) + have been calculated. Whereas the global shape of the potential energy surfaces is obtained in reasonable agreement with existing ab initio data, at least if scaling is introduced, there are marked differences in the details, e.g. the angular dependences and splitting of the first and second excited-state potential energy surfaces. The dependence of the results on mixing parameters and scaling as well as implications concerning the predictive power of the DIM method are discussed.

Ab initiocalculations of transition metal complexes

The He(I) and He(II) photoelectron spectra of Fe(CO)2(NO)2 are reported and suggest a different assignment of the low energy region of the spectrum from that given by previous SCF calculations. Extended basis set calculations are described which include limited correlation effects in the ground and ionic states. These calculations show that it is the greater correlation energy associated with the Fe-NO π bonding molecular orbitals, compared to the iron 3d orbitals, which is responsible for the incorrect ordering of the ionic states given by SCF calculations.

ChemInform Abstract: HARTREE‐FOCK MINIMAL AND EXTENDED BASIS SET AND CONFIGURATION INTERACTION CALCULATIONS ON THE HYDROBORATION REACTION

Chemischer InformationsdienstVolume 10, Issue 36 Physical Organic Chemistry ChemInform Abstract: HARTREE-FOCK MINIMAL AND EXTENDED BASIS SET AND CONFIGURATION INTERACTION CALCULATIONS ON THE HYDROBORATION REACTION K. R. SUNDBERG, K. R. SUNDBERGSearch for more papers by this authorG. D. GRAHAM, G. D. GRAHAMSearch for more papers by this authorW. N. LIPSCOMB, W. N. LIPSCOMBSearch for more papers by this author K. R. SUNDBERG, K. R. SUNDBERGSearch for more papers by this authorG. D. GRAHAM, G. D. GRAHAMSearch for more papers by this authorW. N. LIPSCOMB, W. N. LIPSCOMBSearch for more papers by this author First published: September 4, 1979 https://doi.org/10.1002/chin.197936098AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue36September 4, 1979 RelatedInformation

Hartree-Fock minimal and extended basis set and configuration interaction calculations on the hydroboration reaction

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTHartree-Fock minimal and extended basis set and configuration interaction calculations on the hydroboration reactionKenneth R. Sundberg, Glenn D. Graham, and William N. LipscombCite this: J. Am. Chem. Soc. 1979, 101, 11, 2863–2869Publication Date (Print):May 1, 1979Publication History Published online1 May 2002Published inissue 1 May 1979https://doi.org/10.1021/ja00505a010RIGHTS & PERMISSIONSArticle Views98Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (773 KB) Get e-Alerts Get e-Alerts

ChemInform Abstract: EXTENDED BASIS SET CALCULATIONS OF NONLINEAR SUSCEPTIBILITIES OF CONJUGATED HYDROCARBONS

Chemischer InformationsdienstVolume 10, Issue 13 Physical Organic Chemistry ChemInform Abstract: EXTENDED BASIS SET CALCULATIONS OF NONLINEAR SUSCEPTIBILITIES OF CONJUGATED HYDROCARBONS E. F. MCINTYRE, E. F. MCINTYRESearch for more papers by this authorH. F. HAMEKA, H. F. HAMEKASearch for more papers by this author E. F. MCINTYRE, E. F. MCINTYRESearch for more papers by this authorH. F. HAMEKA, H. F. HAMEKASearch for more papers by this author First published: March 27, 1979 https://doi.org/10.1002/chin.197913088AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume10, Issue13March 27, 1979 RelatedInformation

Extended basis set calculations of nonlinear susceptibilities of conjugated hydrocarbons

We reconsidered perturbation treatments of molecular eigenstates by expanding in terms of other molecular eigenstates. This constitutes an improvement over a previously reported treatment where we considered molecular orbitals which were expanded in terms of other molecular orbitals. In the present paper, we take the ground state molecular wavefunction as a single determinant SCF function. Fourth order energy perturbations are then obtained as a sum of contributions from singly and doubly excited molecular configurations. We evaluated the various fourth-order energy perburbations and corresponding third-order electric susceptibilities for a group of about 30 aromatic hydrocarbons and for a group of linear conjugated hydrocarbons. Our results are roughly consistent with the limited experimental information that is available for these molecules.

A critical test of the usefulness of simons type model potentials in molecular calculations

Simons type pseudopotentials were employed in extended basis set calculations of Li + 2, Na + 2 and K + 2, using 1s, 2s, 3s and 2pσ functions on each center. Calculations of this type give inaccurate results because the pseudopotential is too repulsive in the atomic valence region. These results clearly show that Simons type pseudopotentials are not useful for extensive molecular calculations.

Ab-initio studies of fluoroxytrifluoromethane geometry and electronic structure

Ab-initio molecular orbital calculations using both minimal or STO-3G and extended or 4-31G basis sets have been applied to fluoroxytrifluormethane. Complete geometry optimizations using both basis sets have been applied to this molecule and the calculated structural parameters have been compared to the electron diffraction data. The extended basis set calculations are found to be in much better overall agreement with experiment although the minimal basis set does reproduce the angular parameters well, including the tilt angle. The barrier to the CF 3 torsion has been computed and it compares favorably with the microwave spectral value. The electronic structure of CF 3OF and some related molecules have been examined by partitioning the electrons according to the method of Mulliken. The highest occupied orbital in CF 3OF is found to be largely an O-F π * orbital and the O-F bond is also found to be the least ionic and weakest bond in the molecule. The computed dipole moment of CF 3OF agrees well with the experimental value.

The electronic structure of peracids. Functional models for cytochrome p-450

An extensive set of ground state ab initio and semiempirical molecular orbital calculations has been performed on both peroxytrifluoroacetic and peroxyacetic acids. The equilibrium geometry of peroxyacetic acid was calculated with the STO-3G and MINDO/3 methods, and peroxide rotational barriers for both peracids were obtained with STO-3G and PCILO. Extended basis set calculations with the 6-31G ** basis were performed for both peracids to compare the electronic structures of these two compounds. Electrostatic potential maps in the region of the peroxide bonds of both peracids were also calculated using INDO wavefunetions. These results are discussed with respect to the enhanced reactivity of peroxytrifluoracetic acid relative to peroxyacetic acid and the nature of the oxygen electrophilicity in these compounds and by analogy in cytochrome P-450, for which peroxytrifluoroacetic acid is considered to be an effective chemical model.

Some theoretical aspects of vibrational fine structure accompanying core ionizations in N2 and CO

Ab initio calculations have been carried out on CO and N2 and the relevant core hole states with different basis sets to investigate differences in geometries and force constants. From these calculations vibrational band profiles of the core level ESCA spectra for these molecules have been interpreted, obviating the need to rely on data pertaining to the equivalent core species. The agreement with experimental profiles is excellent. The O1s level of CO which has not been subjected to detailed theoretical analysis previously, is predicted to show substantial vibrational structure in excellent agreement with recently acquired experimental data. The effect of temperature on the band profiles has also been considered. Theoretically derived core binding and relaxation energies of these systems have been investigated both as a function of basis set, and of internuclear distance. Density difference contours have been computed and give a straightforward pictorial representation of the substantial electron reorganizations accompanying core ionizations. Small basis sets with valence exponents appropriate to the equivalent core species when used in hole state calculations describe bond lengths, force constants, core binding energies and relaxation energies with an accuracy comparable to that appropriate to the corresponding extended basis set calculations.

Structure de l'ion fluoronium FH et chemin de la protonation du fluorure d'hydrogene

AbstractThe structure of the ion FH is investigated on the basis of semiempirical (INDO) and nonempirical (extended gaussian basis set) calculations. In agreement with experiment, both methods predict that, when going from FH to FH, there is a lengthening of the FH bond; also in agreement with infrared analysis, the calculations indicate a bent structure for the fluoronium ion (valence angle at about 120°). The analysis of the FH protonation path reveals the existence of a potential barrier which is exclusively produced by solvation effects; the dependence of the proton affinity of FH on the dielectric constant of the reaction medium is also discussed.

Theoretical study of the electronic structure of the diboron and tetraboron tetrahalides

The electronic structures of B2F4, B2Cl4, B4F4 and B4Cl4 are discussed using the results of all electron ab initio SCF–MO calculations in bases of Gaussian type functions. The diboron tetrahalides are predicted to have a staggered D2d configuration, with a barrier to rotation of 1.48 kcal/mol for B2Cl4 and 0.39 kcal/mol for B2F4. The calculated wavefunctions from both minimal and extended basis set calculations are used to interpret the low energy photoelectron spectrum of B4Cl4. The bonding in these molecules is analysed by electron density difference maps and by transforming the valence SCF–MOs to localized orbitals using the method due to Boys. Reasons for the observed stability of B4Cl4 and presumed instability of B4F4 are discussed.

Calculations of the barrier to internal rotation in ethyl flouride: A comparison with ethane

The barriers to internal rotation in ethyl flouride and ethane have been calculated and compared using two types of basis sets. Minimum basis set calculations predict the barrier in ethyl fluoride to be 0.5 kcal/mole smaller than the ethane barrier. Extended basis set calculations give barriers of 3.4 and 3.3 kcal/mole for ethyl fluoride and ethane. These results are in better agreement with the experimental values of 3.3 and 3.0 kcal/mole. The changes in the wave function due to increasing the size of the basis set are studied and discussed.