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Martin Headgordon - One of the best experts on this subject based on the ideXlab platform.

  • clarifying the quantum mechanical origin of the covalent chemical bond
    Nature Communications, 2020
    Co-Authors: Daniel S Levine, Martin Headgordon
    Abstract:

    Lowering of the electron kinetic energy (KE) upon initial encounter of radical fragments has long been cited as the primary origin of the covalent chemical bond based on Ruedenberg's pioneering analysis of H[Formula: see text] and H2 and presumed generalization to other bonds. This work reports KE changes during the initial encounter corresponding to bond formation for a range of different bonds; the results demand a re-evaluation of the role of the KE. Bonds between heavier elements, such as H3C-CH3, F-F, H3C-OH, H3C-SiH3, and F-SiF3 behave in the opposite way to H[Formula: see text] and H2, with KE often increasing on bringing radical fragments together (though the total energy change is substantially stabilizing). The origin of this difference is Pauli Repulsion between the electrons forming the bond and core electrons. These results highlight the fundamental role of constructive quantum interference (or resonance) as the origin of chemical bonding. Differences between the interfering states distinguish one type of bond from another.

  • unraveling substituent effects on frontier orbitals of conjugated molecules using an absolutely localized molecular orbital based analysis
    Chemical Science, 2018
    Co-Authors: Martin Headgordon, Yihan Shao
    Abstract:

    It is common to introduce electron-donating or electron-withdrawing substituent groups into functional conjugated molecules (such as dyes) to tune their electronic structure properties (such as frontier orbital energy levels) and photophysical properties (such as absorption and emission wavelengths). However, there lacks a generally applicable tool that can unravel the underlying interactions between orbitals from a substrate molecule and those from its substituents in modern electronic structure calculations, despite the long history of qualitative molecular orbital theory. In this work, the absolutely localized molecular orbitals (ALMO) based analysis is extended to analyze the effects of substituent groups on the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of a given system. This provides a bottom-up avenue towards quantification of effects from distinct physical origins (e.g. permanent electrostatics/Pauli Repulsion, mutual polarization, inter-fragment orbital mixing). For the example case of prodan (a typical dye molecule), it is found that inter-fragment orbital mixing plays a key role in narrowing the HOMO–LUMO gap of the naphthalene core. Specifically, an out-of-phase mixing of high-lying occupied orbitals on the naphthalene core and the dimethylamino group leads to an elevated HOMO, whereas an in-phase combination of LUMOs on the naphthalene core and the propionyl group lowers the LUMO energy of the entire molecule. We expect this ALMO-based analysis to bridge the gap between concepts from qualitative orbital interaction analysis and quantitative electronic structure calculations.

  • energy decomposition analysis for exciplexes using absolutely localized molecular orbitals
    Journal of Chemical Physics, 2018
    Co-Authors: Qinghui Ge, Martin Headgordon
    Abstract:

    An energy decomposition analysis (EDA) scheme is developed for understanding the intermolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized molecular orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli Repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexes (e.g., formamide-water, pyridine/pyrimidine-water) and halide (F−, Cl−)-water clusters that involve charge-transfer-to-solvent excitations.An energy decomposition analysis (EDA) scheme is developed for understanding the intermolecular interaction involving molecules in their excited states. The EDA utilizes absolutely localized molecular orbitals to define intermediate states and is compatible with excited state methods based on linear response theory such as configuration interaction singles and time-dependent density functional theory. The shift in excitation energy when an excited molecule interacts with the environment is decomposed into frozen, polarization, and charge transfer contributions, and the frozen term can be further separated into Pauli Repulsion and electrostatics. These terms can be added to their counterparts obtained from the ground state EDA to form a decomposition of the total interaction energy. The EDA scheme is applied to study a variety of systems, including some model systems to demonstrate the correct behavior of all the proposed energy components as well as more realistic systems such as hydrogen-bonding complexe...

  • characterizing the interplay of Pauli Repulsion electrostatics dispersion and charge transfer in halogen bonding with energy decomposition analysis
    Physical Chemistry Chemical Physics, 2018
    Co-Authors: Jonathan Thirman, Elric Engelage, Stefan M Huber, Martin Headgordon
    Abstract:

    The halogen bond is a class of non-covalent interaction that has attracted considerable attention recently. A widespread theory for describing them is the σ-hole concept, which predicts that the strength of the interaction is proportional to the size of the σ-hole, a region of positive electrostatic potential opposite a σ bond. Previous work shows that in the case of CX3I, with X equal to F, Cl, Br, and I, the σ-hole trend is exactly opposite to the trend in binding energy with common electron pair donors. Using energy decomposition analysis (EDA) applied to a potential energy scan as well as the recent adiabatic EDA technique, we show that the observed trend is a result of charge transfer. Therefore a picture of the halogen bond that excludes charge transfer cannot be complete, and permanent and induced electrostatics do not always provide the dominant stabilizing contributions to halogen bonds. Overall, three universally attractive factors, polarization, dispersion and charge transfer, together with permanent electrostatics, which is usually attractive, drive halogen bonding, against Pauli Repulsion.

  • assessing many body contributions to intermolecular interactions of the amoeba force field using energy decomposition analysis of electronic structure calculations
    Journal of Chemical Physics, 2017
    Co-Authors: Omar N A Demerdash, Martin Headgordon, Teresa Headgordon
    Abstract:

    In this work, we evaluate the accuracy of the classical AMOEBA model for representing many-body interactions, such as polarization, charge transfer, and Pauli Repulsion and dispersion, through comparison against an energy decomposition method based on absolutely localized molecular orbitals (ALMO-EDA) for the water trimer and a variety of ion-water systems. When the 2- and 3-body contributions according to the many-body expansion are analyzed for the ion-water trimer systems examined here, the 3-body contributions to Pauli Repulsion and dispersion are found to be negligible under ALMO-EDA, thereby supporting the validity of the pairwise-additive approximation in AMOEBA’s 14-7 van der Waals term. However AMOEBA shows imperfect cancellation of errors for the missing effects of charge transfer and incorrectness in the distance dependence for polarization when compared with the corresponding ALMO-EDA terms. We trace the larger 2-body followed by 3-body polarization errors to the Thole damping scheme used in A...

Benedetta Mennucci - One of the best experts on this subject based on the ideXlab platform.

  • on the effect of Pauli Repulsion and dispersion on static molecular polarizabilities and hyperpolarizabilities in solution
    Chemical Physics Letters, 1998
    Co-Authors: Benedetta Mennucci, Claudio Amovilli, Jacopo Tomasi
    Abstract:

    Abstract A study of the effect of Repulsion and dispersion solute–solvent interactions on solute (hyper)polarizabilities is reported. The calculations have been performed within the polarizable continuum model and include the electrostatic contribution. The results show a negligible effect due to dispersion while for Repulsion a substantial effect, especially on the second hyperpolarizabilities, has been found.

  • continuum solvation models a new approach to the problem of solute s charge distribution and cavity boundaries
    Journal of Chemical Physics, 1997
    Co-Authors: Benedetta Mennucci, Jacopo Tomasi
    Abstract:

    In continuum solvation models the definition of a cavity that embeds the solute molecule leads to problems related to the portion of solute’s electronic charge lying outside its boundaries (charge tails). The correction strategies developed so far can be shown to work insufficiently, since they only correct the global charge defect, but lead to considerable local errors. The present paper will be focused on the theoretical and technical aspects of this problem, and it will present in detail a new method which allows a very refined treatment of solute’s charge tails in the outer space; some numerical results of solutes in water will be shown and discussed. As further analyses, the introduction of Pauli Repulsion term will be considered, and the implications all these effects have on molecular properties, such as (hyper)polarizabilities, numerically evaluated. The new approach has been implemented within the framework of the polarizable continuum model (PCM).

  • Self-Consistent-Field Calculation of Pauli Repulsion and Dispersion Contributions to the Solvation Free Energy in the Polarizable Continuum Model
    The Journal of Physical Chemistry B, 1997
    Co-Authors: Claudio Amovilli, Benedetta Mennucci
    Abstract:

    By using the theory of intermolecular forces, two new expressions for Pauli Repulsion and dispersion contributions to the solvation free energy are derived. These expressions contain explicitly the solute electron density and, therefore, can be used directly in the SCF calculation of the solute wave function within the polarizable continuum model (PCM). The final expressions are very simple and include also some intrinsic solvent properties which are, for Repulsion, the density, the molecular weight, the number of valence electrons, and for dispersion, the refractive index and the ionization potential. This new approach does not depend on any given intermolecular potential and it can be adapted to any choice of basis set. For small-size basis sets, even minimal, the dispersion contribution is obtained in two steps and includes the effect of adding diffuse and polarization functions, not used in the wave function itself. This method has been implemented in our HONDO package, in a version which includes the...

Jacopo Tomasi - One of the best experts on this subject based on the ideXlab platform.

  • on the effect of Pauli Repulsion and dispersion on static molecular polarizabilities and hyperpolarizabilities in solution
    Chemical Physics Letters, 1998
    Co-Authors: Benedetta Mennucci, Claudio Amovilli, Jacopo Tomasi
    Abstract:

    Abstract A study of the effect of Repulsion and dispersion solute–solvent interactions on solute (hyper)polarizabilities is reported. The calculations have been performed within the polarizable continuum model and include the electrostatic contribution. The results show a negligible effect due to dispersion while for Repulsion a substantial effect, especially on the second hyperpolarizabilities, has been found.

  • continuum solvation models a new approach to the problem of solute s charge distribution and cavity boundaries
    Journal of Chemical Physics, 1997
    Co-Authors: Benedetta Mennucci, Jacopo Tomasi
    Abstract:

    In continuum solvation models the definition of a cavity that embeds the solute molecule leads to problems related to the portion of solute’s electronic charge lying outside its boundaries (charge tails). The correction strategies developed so far can be shown to work insufficiently, since they only correct the global charge defect, but lead to considerable local errors. The present paper will be focused on the theoretical and technical aspects of this problem, and it will present in detail a new method which allows a very refined treatment of solute’s charge tails in the outer space; some numerical results of solutes in water will be shown and discussed. As further analyses, the introduction of Pauli Repulsion term will be considered, and the implications all these effects have on molecular properties, such as (hyper)polarizabilities, numerically evaluated. The new approach has been implemented within the framework of the polarizable continuum model (PCM).

Claudio Amovilli - One of the best experts on this subject based on the ideXlab platform.

Karlheinz Ernst - One of the best experts on this subject based on the ideXlab platform.

  • Pauli Repulsion versus van der waals interaction of indenocorannulene with a cu 111 surface
    Journal of Physical Chemistry B, 2017
    Co-Authors: Laura Zoppi, Quirin S Stockl, Anais Mairena, Oliver Allemann, Jay S Siegel, Kim K Baldridge, Karlheinz Ernst
    Abstract:

    Modification of metal electrode surfaces with functional organic molecules is an important step toward organic electronics. The interaction of the buckybowl indenocorannulene with a Cu(111) surface and the two-dimensional self-assembly on the same surface was studied by means of scanning tunneling microscopy and dispersion-enabled density functional theory. Based on the conjecture of maximizing van der Waals interaction with the surface one would expect the indeno group to be aligned parallel to the surface. Theoretical investigations predict a nonparallel arrangement with the benzo ring of the indeno group located higher above the surface than the bowl rim connected to the indeno group. This adsorbate geometry is due to strong electronic interaction between molecule and surface, including substantial Pauli Repulsion. The long-range ordered monolayer shows differences for two molecules of the unit cell in scanning tunneling microscopy contrast, suggesting either different polar alignments, and therefore a...