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Journal ArticleDOI

Bonded-atom fragments for describing molecular charge densities

01 Jun 1977-Theoretical Chemistry Accounts (Springer-Verlag)-Vol. 44, Iss: 2, pp 129-138
TL;DR: In this article, a general and natural choice is to share the charge density at each point among the several atoms in proportion to their free-atom densities at the corresponding distances from the nuclei.
Abstract: For quantitative description of a molecular charge distribution it is convenient to dissect the molecule into well-defined atomic fragments. A general and natural choice is to share the charge density at each point among the several atoms in proportion to their free-atom densities at the corresponding distances from the nuclei. This prescription yields well-localized bonded-atom distributions each of which closely resembles the molecular density in its vicinity. Integration of the atomic deformation densities — bonded minus free atoms — defines net atomic charges and multipole moments which concisely summarize the molecular charge reorganization. They permit calculation of the external electrostatic potential and of the interaction energy between molecules or between parts of the same molecule. Sample results for several molecules indicate a high transferability of net atomic charges and moments.
Citations
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TL;DR: Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn, a multifunctional program for wavefunction analysis.
Abstract: Multiwfn is a multifunctional program for wavefunction analysis. Its main functions are: (1) Calculating and visualizing real space function, such as electrostatic potential and electron localization function at point, in a line, in a plane or in a spatial scope. (2) Population analysis. (3) Bond order analysis. (4) Orbital composition analysis. (5) Plot density-of-states and spectrum. (6) Topology analysis for electron density. Some other useful utilities involved in quantum chemistry studies are also provided. The built-in graph module enables the results of wavefunction analysis to be plotted directly or exported to high-quality graphic file. The program interface is very user-friendly and suitable for both research and teaching purpose. The code of Multiwfn is substantially optimized and parallelized. Its efficiency is demonstrated to be significantly higher than related programs with the same functions. Five practical examples involving a wide variety of systems and analysis methods are given to illustrate the usefulness of Multiwfn. The program is free of charge and open-source. Its precompiled file and source codes are available from http://multiwfn.codeplex.com.

17,273 citations

Journal ArticleDOI
TL;DR: In this paper, a method for accurate and efficient local density functional calculations (LDF) on molecules is described and presented with results using fast convergent threedimensional numerical integrations to calculate the matrix elements occurring in the Ritz variation method.
Abstract: A method for accurate and efficient local density functional calculations (LDF) on molecules is described and presented with results The method, Dmol for short, uses fast convergent three‐dimensional numerical integrations to calculate the matrix elements occurring in the Ritz variation method The flexibility of the integration technique opens the way to use the most efficient variational basis sets A practical choice of numerical basis sets is shown with a built‐in capability to reach the LDF dissociation limit exactly Dmol includes also an efficient, exact approach for calculating the electrostatic potential Results on small molecules illustrate present accuracy and error properties of the method Computational effort for this method grows to leading order with the cube of the molecule size Except for the solution of an algebraic eigenvalue problem the method can be refined to quadratic growth for large molecules

8,673 citations

Journal ArticleDOI
TL;DR: The “Activation‐strain TS interaction” (ATS) model of chemical reactivity is reviewed as a conceptual framework for understanding how activation barriers of various types of reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis.
Abstract: We present the theoretical and technical foundations of the Amsterdam Density Functional (ADF) program with a survey of the characteristics of the code (numerical integration, density fitting for the Coulomb potential, and STO basis functions). Recent developments enhance the efficiency of ADF (e.g., parallelization, near order-N scaling, QM/MM) and its functionality (e.g., NMR chemical shifts, COSMO solvent effects, ZORA relativistic method, excitation energies, frequency-dependent (hyper)polarizabilities, atomic VDD charges). In the Applications section we discuss the physical model of the electronic structure and the chemical bond, i.e., the Kohn–Sham molecular orbital (MO) theory, and illustrate the power of the Kohn–Sham MO model in conjunction with the ADF-typical fragment approach to quantitatively understand and predict chemical phenomena. We review the “Activation-strain TS interaction” (ATS) model of chemical reactivity as a conceptual framework for understanding how activation barriers of various types of (competing) reaction mechanisms arise and how they may be controlled, for example, in organic chemistry or homogeneous catalysis. Finally, we include a brief discussion of exemplary applications in the field of biochemistry (structure and bonding of DNA) and of time-dependent density functional theory (TDDFT) to indicate how this development further reinforces the ADF tools for the analysis of chemical phenomena. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 931–967, 2001

8,490 citations

Journal ArticleDOI
TL;DR: In the last few years, the analysis of molecular crystal structures using tools based on Hirshfeld surfaces has rapidly gained in popularity as mentioned in this paper, which represents an attempt to venture beyond the current paradigm of nuclear distances and angles, crystal packing diagrams with molecules represented via various models, and to view molecules as organic wholes.
Abstract: In the last few years the analysis of molecular crystal structures using tools based on Hirshfeld surfaces has rapidly gained in popularity. This approach represents an attempt to venture beyond the current paradigm—internuclear distances and angles, crystal packing diagrams with molecules represented via various models, and the identification of close contacts deemed to be important—and to view molecules as “organic wholes”, thereby fundamentally altering the discussion of intermolecular interactions through an unbiased identification of all close contacts.

4,930 citations

Journal ArticleDOI
TL;DR: This chapter discusses the development of DFT as a tool for Calculating Atomic andMolecular Properties and its applications, as well as some of the fundamental and Computational aspects.
Abstract: I. Introduction: Conceptual vs Fundamental andComputational Aspects of DFT1793II. Fundamental and Computational Aspects of DFT 1795A. The Basics of DFT: The Hohenberg−KohnTheorems1795B. DFT as a Tool for Calculating Atomic andMolecular Properties: The Kohn−ShamEquations1796C. Electronic Chemical Potential andElectronegativity: Bridging Computational andConceptual DFT1797III. DFT-Based Concepts and Principles 1798A. General Scheme: Nalewajski’s ChargeSensitivity Analysis1798B. Concepts and Their Calculation 18001. Electronegativity and the ElectronicChemical Potential18002. Global Hardness and Softness 18023. The Electronic Fukui Function, LocalSoftness, and Softness Kernel18074. Local Hardness and Hardness Kernel 18135. The Molecular Shape FunctionsSimilarity 18146. The Nuclear Fukui Function and ItsDerivatives18167. Spin-Polarized Generalizations 18198. Solvent Effects 18209. Time Evolution of Reactivity Indices 1821C. Principles 18221. Sanderson’s Electronegativity EqualizationPrinciple18222. Pearson’s Hard and Soft Acids andBases Principle18253. The Maximum Hardness Principle 1829IV. Applications 1833A. Atoms and Functional Groups 1833B. Molecular Properties 18381. Dipole Moment, Hardness, Softness, andRelated Properties18382. Conformation 18403. Aromaticity 1840C. Reactivity 18421. Introduction 18422. Comparison of Intramolecular ReactivitySequences18443. Comparison of Intermolecular ReactivitySequences18494. Excited States 1857D. Clusters and Catalysis 1858V. Conclusions 1860VI. Glossary of Most Important Symbols andAcronyms1860VII. Acknowledgments 1861VIII. Note Added in Proof 1862IX. References 1865

3,890 citations

References
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Journal ArticleDOI
TL;DR: In this article, the authors show how electroaffinity and other data can be used in the approximate determination of the polarities of molecular orbitals and so of bonds, the results being expressed both in terms of coefficients in LCAO molecular orbits and the effective charges transferred.
Abstract: A convenient criterion for defining equal electronegativity of two atoms is stated in terms of coefficients in LCAO approximate molecular orbitals. Connections between relative electronegativities, coefficients in LCAO orbitals, effective charges on atoms in partially polar molecules, and dipole moments, are then analyzed, and various equations are obtained expressing these connections. The discussion is largely applicable to polyatomic as well as to diatomic molecules. A theoretical derivation is given for an empirical equation, found by Pauling, which forms a basis for the latter's approximate scale of relative electronegativities. Pauling's and other possible approximate scales are discussed, and it is shown how an approximate ``absolute electroaffinity'' can conveniently be defined on each scale. A very rough theoretical justification is given for the empirically observed proportionality between relative electronegativities obtained from Pauling's and from the writer's scale. The necessary existence of a ``homopolar dipole'' contribution to the electric moment of any bond is shown, provided the atoms forming the bond are of unequal size. By ``homopolar dipole'' is meant a contribution which would not vanish, for atoms of unequal size, even if they are of equal electroaffinity. Dipole moments of H2O, NH3 and HX are briefly discussed. It is concluded that the dipole moment scale of electronegativity is probably not well founded. An important object of the paper is to show how electroaffinity and other data can be used in the approximate determination of the polarities of molecular orbitals and so of bonds, the results being expressed both in terms of coefficients in LCAO molecular orbitals and in terms of effective charges transferred. Applications are made to the electronic structures of various diatomic molecules, especially HI, HI+, HO—, ClO—.

366 citations

Journal ArticleDOI
TL;DR: In this article, a series of single-determinant SCF-LCAO-MO wavefunctions were used to study the changes that occur in the electron density as the Hartree-Fock solution is approached.
Abstract: Electron density maps and their appropriately weighted analogs (e.g., dipole‐weighted density map) are found to provide a consistent and useful tool for the analysis and the comparison of atomic and molecular charge distributions obtained with different wavefunctions. Specific applications are made to hydrogen fluoride, for which a series of single‐determinant SCF—LCAO—MO wavefunctions permit a study of the changes that occur in the electron density as the Hartree—Fock solution is approached. An examination of alternative basis‐set functions of essentially the same size and the same energy shows that significantly different charge distributions can result; this points out the need for a careful selection of basis functions in large scale molecular calculations. It is found also that the charge density fluctuations from one basis set to another can be as large as the effects of chemical binding. Comparisons between density‐map and population‐analysis results indicate that considerable caution must be used in employing the latter for the interpretation of complicated wavefunctions.Various methods for summarizing wavefunctions in terms of characteristic parameters of the charge distribution are considered. The forces acting on the nuclei are analyzed in relation to the Hellmann‐Feynman theorem and a necessary condition on the exact molecular Hartree—Fock solution is obtained. Although none of the presently available wavefunctions for HF and LiF satisfy the condition to a high degree of accuracy, refinements in the wavefunctions are shown to yield improved results.

126 citations