Natural bond orbital methods

High-level quantum chemical calculations reported here predict the existence and remarkable stability, of chemically-bound xenon atoms in fibrous silica. The results may support the suggestion of Sanloup and coworkers that chemically-bound xenon and silica account for the problem of ''missing xenon'' (by a factor of 20!) from the atmospheres of Earth and Mars. So far, the host silica was assumed to be quartz, which is in contradiction with theory. The xenon-fibrous silica molecule is computed to be stable well beyond room temperature. The calculated Raman spectra of the species agree well with the main features of the experiments by Sanloup et al. The results predict computationally the existence of a new family of noble-gas containing materials. The fibrous silica species are finite molecules, their laboratory preparation should be feasible, and potential applications are possible.

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“…38 Partial charges and bond orders were calculated using NBO 39,40 analysis. In all calculations the internal coordinates were used.…”

Section: Methodsmentioning

confidence: 99%

Chemically-bound xenon in fibrous silica

Kalinowski

Räsänen

Gerber

2014

Phys. Chem. Chem. Phys.

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“…Such components typically include permanent electrostatics, corresponding to interactions between charges and/or multipole moments, induced electrostatics associated with polarisation, Pauli repulsions associated with interactions between filled orbitals, and dative or donor acceptor interactions associated with interactions between filled and empty orbitals. By far the best-known EDA approach is the natural bond orbital (NBO) suite of methods due to Weinhold and co-workers [395][396][397][398], which Q-CHEM supports via a standard interface to the current version of the NBO package.…”

Section: Energy Decomposition Analysismentioning

confidence: 99%

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

Shao¹,

Gan²,

Epifanovsky³

et al. 2014

Molecular Physics

2,746

2,077

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A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and openshell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller-Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr 2 dimer, exploring zeolitecatalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.Keywords quantum chemistry, software, electronic structure theory, density functional theory, electron correlation, computational modelling, Q-Chem Disciplines Chemistry CommentsThis article is from Molecular Physics: An International Journal at the Interface Between Chemistry and Physics 113 (2015): 184, doi:10.1080/00268976.2014. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. Authors 185A summary of the technical advances that are incorporated in the fourth major release of the Q-CHEM quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller-Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly corre...

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“…[43] It is useful to r study donor-acceptor interactions. [44] Interestingly, we found that the lone pair of N1 interacts with both C1-C2 and C1-C3 (see Figure 2 for atom numbering) anti-bonding orbitals with a concomitant second-order stabilization energy of 1.42 kJ mol-1 for each interaction and the energetic difference between the lp and s* antibonding orbitals is 1.22. Therefore, the stabilization energy that can be attributed to orbital effects (2.84 kJ mol-1) is small compared with the total interaction energy (-33.8 kJ mol-1) computed for this dimer.…”

Section: Figurementioning

confidence: 82%

Nature of Noncovalent Carbon‐Bonding Interactions Derived from Experimental Charge‐Density Analysis

2015

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In an effort to better understand the nature of noncovalent carbon-bonding interactions, we undertook accurate high-res-olution X-ray diffraction analysis of single crystals of 1,1,2,2-tetracyanocyclopropane. We selected this compound to study the fundamental characteristics of carbon-bonding interactions, because it provides accessible s holes. The study required extremely accurate experimental diffraction data, because the in-teraction of interest is weak. The electron-density distribution around the carbon nuclei, as shown by the experimental maps of the electrophilic bowl defined by a (CN)2C-C(CN)2 unit, was assigned as the origin of the interaction. This fact was also evidenced by plotting the D21(r) distribution. Taken together, the obtained results clearly indicate that noncovalent carbon bonding can be explained as an interaction between confront-ed oppositely polarized regions. The interaction is, thus elec-trophilic-nucleophilic (electrostatic) in nature and unambigu-ously considered as attractive.Attractive intermolecular electrostatic interactions encompass electron-rich and electron-poor regions of two molecules that complement each other.[1] Electron-rich entities are typically anions or lone-pair electrons and the most well-known elec-tron-poor entity is the hydrogen atom. Consequently, hydro-gen bonding is undoubtedly the most exploited supramolec-ular interaction.[2] Nowadays, another common electron-poor entity is attracting increasing attention in the literature. It is the 's hole', which can be defined as an electron-deficient anti-bonding orbital of a covalent bond. [3-13] Such regions of posi-tive electrostatic potential have been largely studied for atoms of groups V, VI, and VII (pnicogen, [14,15] chalcogen, [16][17][18] and hal-ogen [19-22] bonding, respectively [23] ) . Many reviews have described halogen bonding in detail, which is the best-known s-hole interaction. [6,[19][20][21][22] More recently, s-hole complexes with atoms of group IV, the tetrel (Tr) atoms, have been described, [24][25][26][27][28][29] and mostly focus on the heavier Tr atoms as tetrel-bond donors, leaving noncovalent carbon bonding much less studied. [30][31][32] In an sp 3 -hybridized electron-deficient C atom, there is only limited space available for an electron-rich guest molecule to nest itself. [31,32] To exem-plify this, we have represented in Figure 1 (right) the MEP sur- Figure 1.face of 1,1,2,2-tetracyanoethane (staggered conformation). The s hole is small and it is surrounded by negative belts, which hinder interactions with any concentration of negative charge (lone pair or anion). However, if the MEP surface is computed in the eclipsed conformation (C2v), the resulting s hole is more exposed and the electrostatic potential is considerable more positive. As a matter of fact, it has been recently demonstrated that the (CN) 2 C-C(CN) 2 motif of 1,1,2,2-tetracyanocyclopropane is an excellent carbon-bond donor, because the s hole is very exposed.[33] Moreover, it is synthetically accessible and the N_ C...

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Natural bond orbital methods

Cited by 1,327 publications

References 75 publications

Chemically-bound xenon in fibrous silica

Chemically-bound xenon in fibrous silica

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

Nature of Noncovalent Carbon‐Bonding Interactions Derived from Experimental Charge‐Density Analysis

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