Natural bond orbital analysis of nearHartree-Fock water dimer
01 Jan 2013-
TL;DR: In this article, the authors carried out a natural bond orbital analysis of hydrogen bonding in the water dimer for the near Hartree-Fock wave function of Popkie, Kistenmacher, and Clementi, extending previous studies based on smaller basis sets and less realistic geometry.
Abstract: We have carried out a natural bond orbital analysis of hydrogen bonding in the water dimer for the near‐Hartree–Fock wave function of Popkie, Kistenmacher, and Clementi, extending previous studies based on smaller basis sets and less realistic geometry. We find that interactions which may properly be described as ‘‘charge transfer’’ (particularly the n‐σ*OH interaction along the H‐bond axis) play a critical role in the formation of the hydrogen bond, and without these interactions the water dimer would be 3–5 kcal/mol repulsive at the observed equilibrium distance. We discuss this result in relationship to Klemperer’s general picture of the bonding in van der Waals molecules, and to previous theoretical analyses of hydrogen bonding by the method of Kitaura and Morokuma.
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TL;DR: In this paper, a method of "natural population analysis" was developed to calculate atomic charges and orbital populations of molecular wave functions in general atomic orbital basis sets, which seems to exhibit improved numerical stability and to better describe the electron distribution in compounds of high ionic character.
Abstract: A method of ‘‘natural population analysis’’ has been developed to calculate atomic charges and orbital populations of molecular wave functions in general atomic orbital basis sets. The natural analysis is an alternative to conventional Mulliken population analysis, and seems to exhibit improved numerical stability and to better describe the electron distribution in compounds of high ionic character, such as those containing metal atoms. We calculated ab initio SCF‐MO wave functions for compounds of type CH3X and LiX (X=F, OH, NH2, CH3, BH2, BeH, Li, H) in a variety of basis sets to illustrate the generality of the method, and to compare the natural populations with results of Mulliken analysis, density integration, and empirical measures of ionic character. Natural populations are found to give a satisfactory description of these molecules, providing a unified treatment of covalent and extreme ionic limits at modest computational cost.
8,332 citations
TL;DR: The method of natural localized molecular orbitals (NLMOs) as discussed by the authors is an extension of the previously developed natural atomic orbital (NAO) and natural bond orbital (NBO) methods, and uses only the information contained in the one particle density matrix.
Abstract: The method of natural localized molecular orbitals (NLMOs) is presented as a novel and efficient technique for obtaining LMOs for SCF and CI wave functions. It is an extension of the previously developed natural atomic orbital (NAO) and natural bond orbital (NBO) methods, and uses only the information contained in the one‐particle density matrix. Results are presented for methane and cytosine to indicate that NLMOs closely resemble LMOs obtained by the Boys and Edmiston–Ruedenberg methods, with the exception that the NLMO procedure automatically preserves the MO σ–π separation in planar molecules. The computation time is modest, generally only a small fraction of the SCF computation time. In addition, the derivation of NLMOs from NBOs gives direct insight into the nature of the LMO ‘‘delocalization tails,’’ thus enhancing the role of LMOs as a bridge between chemical intuition and molecular wave functions.
1,948 citations
TL;DR: In this paper, the electronic structure of the radical CH 2 OH was analyzed via the "different hybrids for different spins" natural bond orbital (DHDS NBO) procedure, which finds separate Lewis structures for each of the spin systems.
Abstract: We have carried out ab initio UHF/6-31G* calculations on the hydroxymethyl radical, CH 2 OH, and have found the equilibrium structure to be nearly planar with barriers to internal rotation occurring at staggered and eclipsed geometries, in good agreement with experiment. The electronic structure of the radical was analyzed via the “different hybrids for different spins” natural bond orbital (DHDS NBO) procedure, which finds separate Lewis structures for each of the spin systems. The α spin Lewis structure resembles that of the anion; the β spin Lewis structure resembles the corresponding cation. This simple picture, in conjunction with Bent's rule, allows one to understand the principal electronic factors which dictate the structure of the radical CH 2 group and its torsional and inversion potentials. Charge transfer between oxygen non-bonding orbitals and the empty radical orbital in the β spin system is the dominant interaction determining the torsional potential. Smaller hyperconjugative interactions in the α spin system resemble interactions in closed-shell molecules and directly oppose the effect of radical hyperconjugation, thus illustrating the central idea that open-shell potential energy features result from competition between the two different spin systems.
1,866 citations
TL;DR: The ETS-NOCV scheme offers a compact, qualitative, and quantitative picture of the chemical bond formation within one common theoretical framework and can be widely used for the description of different types of chemical bonds.
Abstract: In the present study we have introduced a new scheme for chemical bond analysis by combining the Extended Transition State (ETS) method [Theor. Chim. Acta 1977, 46, 1] with the Natural Orbitals for Chemical Valence (NOCV) theory [J. Phys. Chem. A 2008, 112, 1933; J. Mol. Model. 2007, 13, 347]. The ETS-NOCV charge and energy decomposition scheme based on the Kohn−Sham approach makes it not only possible to decompose the deformation density, Δρ, into the different components (such as σ, π, δ, etc.) of the chemical bond, but it also provides the corresponding energy contributions to the total bond energy. Thus, the ETS-NOCV scheme offers a compact, qualitative, and quantitative picture of the chemical bond formation within one common theoretical framework. Although, the ETS-NOCV approach contains a certain arbitrariness in the definition of the molecular subsystems that constitute the whole molecule, it can be widely used for the description of different types of chemical bonds. The applicability of the ETS-...
1,193 citations
TL;DR: A method of description of the chemical bonding combining the compactness and intuitive simplicity of Lewis theory with the flexibility and generality of canonical molecular orbital theory is presented, which is called adaptive natural density partitioning.
Abstract: A method of description of the chemical bonding combining the compactness and intuitive simplicity of Lewis theory with the flexibility and generality of canonical molecular orbital theory is presented, which is called adaptive natural density partitioning. The objects of chemical bonding in this method are n-center 2-electron bonds, where n goes from one (lone-pair) to the maximum number of atoms in the system (completely delocalized bonding). The algorithm is a generalization of the natural bonding orbital analysis and is based on the diagonalization of the blocks of the first-order density matrix in the basis of natural atomic orbitals. The results obtained by the application of the algorithm to the systems with non-classical bonding can be readily interpreted from the point of view of aromaticity/antiaromaticity concepts. The considered examples include Li4 cluster and a family of planar boron clusters observed in molecular beams.
1,063 citations
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TL;DR: In this paper, a method for extracting a unique set of atomic hybrids and bond orbitals for a given molecule, thereby constructing its Lewis structure in an a priori manner, is described.
Abstract: From the information contained in the (exact or approximate) first-order density matrix, we describe a method for extracting a unique set of atomic hybrids and bond orbitals for a given molecule, thereby constructing its “Lewis structure” in an a priori manner. These natural hybrids are optimal in a certain sense, are efficiently computed, and seem to agree well with chemical intuition (as summarized, for example, in Bent’s Rule) and with hybrids obtained by other procedures. Using simple INDO-SCF-MO wave functions, we give applications of the natural hybrid orbital analysis to molecules exhibiting a variety of bonding features, including lone pairs, multiple bonds, strained rings, and “bent bonds”, multiple resonance structures, hydrogen bonds, and three-center bonds. Three examples are described in greater detail: (i) “orbital following” during ammonia umbrella inversion, (ii) the dimerization of water molecules, and (iii) the hydrogen-bridged bonds of diborane.
4,338 citations
TL;DR: In this paper, the Hartree-Fock matrix of the supermolecule is used as the basis for the construction of the Fock matrix, and certain blocks of this matrix are set to zero subject to specify boundary conditions of the molecular orbitals, and the resultant matrix is diagonalized iteratively to obtain the desired energy components.
Abstract: A new method is proposed for the analysis of components of molecular interaction energy within the Hartree-Fock approximation. The Hartree-Fock molecular orbitals of the isolated molecules are used as the basis for the construction of Fock matrix of the supermolecule. Then certain blocks of this matrix are set to zero subject to specify boundary conditions of the supermolecule molecular orbitals, and the resultant matrix is diagonalized iteratively to obtain the desired energy components. This method can be considered as an extension of our previous method, but has an advantage in the explicit definition of the charge transfer energy, placing it on an equal footing with the exchange and polarization terms. The new method is compared with existing perturbation methods, and is also applied to the energy and electron density decomposition of (H2O)2.
1,760 citations
TL;DR: In this article, the design, construction, and operation of a new type of microwave spectrograph which allows the measurement of the resonant transitions of transient or otherwise short-lived species is described.
Abstract: We describe the design, construction, and operation of a new type of microwave spectrograph which allows the measurement of the resonant transitions of transient or otherwise short‐lived species. The spectrograph is composed of three parts: a Fabry–Perot cavity, a pulsed supersonic nozzle as a source for the sample, and the pulsed microwave Fourier transform method. Following a detailed discussion of the three above components in the spectrograph, the operation of the entire system is described and several examples are given.
1,371 citations
578 citations