Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties

Njegic, Bosiljka; Gordon, Mark S.

doi:10.1063/1.2395940

Cited by 120 publications

(90 citation statements)

References 66 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…It has been shown previously 23,26 that this choice, when used to create a PES, can produce unreliable frequencies for strongly anharmonic vibrational motions. Indeed, frequencies obtained using the Cartesian coordinate expansion can be several hundred wave numbers too high, even worse than harmonic frequencies.…”

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

“…23,24 While there have been studies regarding the expression of the Hamiltonian in internal coordinates, 25 the present work is addresses methods for generating the potential energy surfaces on the grid by following normal mode displacement vectors.…”

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

“…Indeed, frequencies obtained using the Cartesian coordinate expansion can be several hundred wave numbers too high, even worse than harmonic frequencies. 23 An alternative approach is to generate the PES by using normal mode displacement vectors expressed in internal, as opposed to Cartesian, coordinates. This can be achieved by decomposing normal mode displacement vectors into internal coordinates.…”

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

See 2 more Smart Citations

Predicting accurate vibrational frequencies for highly anharmonic systems

Njegic

Gordon

2008

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

Improvements in the manner in which the potential energy surface (PES) is generated in the vibrational selfconsistent field (VSCF) method have been implemented. The PES can now be computed over a flexible range of displacements and following normal mode displacement vectors expressed in internal rather than Cartesian coordinates, leading to higher accuracy of the calculated vibrational frequencies. The coarse-grained parallelization of the PES calculations, which is computationally by far the most expensive part of the VSCF method, enables the usage of higher levels of theory and larger basis sets. The new VSCF procedure is discussed and applied to three examples, H+3, HNO2, and HNO3, to illustrate its accuracy and applicability. KeywordsNormal modes, Set theory, OzoneBasis sets, Potential energy surfaces Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 129 (2008) Improvements in the manner in which the potential energy surface ͑PES͒ is generated in the vibrational self-consistent field ͑VSCF͒ method have been implemented. The PES can now be computed over a flexible range of displacements and following normal mode displacement vectors expressed in internal rather than Cartesian coordinates, leading to higher accuracy of the calculated vibrational frequencies. The coarse-grained parallelization of the PES calculations, which is computationally by far the most expensive part of the VSCF method, enables the usage of higher levels of theory and larger basis sets. The new VSCF procedure is discussed and applied to three examples, H 3 + , HNO 2 , and HNO 3 , to illustrate its accuracy and applicability.

show abstract

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

Section: Internal Versus Cartesian Normal Mode Displacement Vectorsmentioning

confidence: 99%

See 1 more Smart Citation

Predicting accurate vibrational frequencies for highly anharmonic systems

Njegic

Gordon

2008

The Journal of Chemical Physics

Self Cite

View full text Add to dashboard Cite

show abstract

“…We reduced the scaling of the 3 N dimensional ( N =number of atoms) anharmonic vibrational problem from exponential to linear by solving 3 N one‐dimensional Schrödinger equations for each normal mode independently of all others 17. As finite‐size distortions are needed to calculate the one‐dimensional potentials, the rectilinear normal coordinates need to be represented in curvilinear internal coordinates 18. For example, this ensures that when rotating a molecule relative to the surface, its bond distances and bond angles do not change.…”

mentioning

confidence: 99%

Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

2016

View full text Add to dashboard Cite

The ab initio prediction of reaction rate constants for systems with hundreds of atoms with an accuracy that is comparable to experiment is a challenge for computational quantum chemistry. We present a divide‐and‐conquer strategy that departs from the potential energy surfaces obtained by standard density functional theory with inclusion of dispersion. The energies of the reactant and transition structures are refined by wavefunction‐type calculations for the reaction site. Thermal effects and entropies are calculated from vibrational partition functions, and the anharmonic frequencies are calculated separately for each vibrational mode. This method is applied to a key reaction of an industrially relevant catalytic process, the methylation of small alkenes over zeolites. The calculated reaction rate constants (free energies), pre‐exponential factors (entropies), and enthalpy barriers show that our computational strategy yields results that agree with experiment within chemical accuracy limits (less than one order of magnitude).

show abstract

“…While group theory can elucidate certain global features of energy landscapes, [6][7][8][9] quantitatively accurate potential energy surfaces are needed in many contexts. Thus, chemical reaction rates [10][11][12][13][14][15] are sensitive to energy barriers calculated for transition structures, and thermodynamic properties 16,17 depend on the accuracy of the calculated harmonic and anharmonic frequencies. 18 This demand is motivating work on ab initio methods capable of yielding the desired accuracy 4,5,[19][20][21] and the search for new methodological approaches.…”

Section: Introductionmentioning

confidence: 99%

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

Bytautas

Matsunaga

Nagata

et al. 2007

The Journal of Chemical Physics

134

View full text Add to dashboard Cite

An analytical expression is found for the accurate ab initiopotential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5cm−1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30cm−1 of the experimental value of 12953±8cm−1. The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation,spin-orbit coupling, and scalar relativity. The Dunham analysis [Phys. Rev.41, 721 (1932)] of the spectrum is found to be very accurate. New values are given for the spectroscopic constants. KeywordsAb initio calculations, Dissociation energies, Polynomials, Dissociation, Electron correlation calculations Disciplines Chemistry CommentsThe following article appeared in Journal of Chemical Physics 127 (2007) An analytical expression is found for the accurate ab initio potential energy curve of the fluorine molecule that has been determined in the preceding two papers. With it, the vibrational and rotational energy levels of F 2 are calculated using the discrete variable representation. The comparison of this theoretical spectrum with the experimental spectrum, which had been measured earlier using high-resolution electronic spectroscopy, yields a mean absolute deviation of about 5 cm −1 over the 22 levels. The dissociation energy with respect to the lowest vibrational energy is calculated within 30 cm −1 of the experimental value of 12 953± 8 cm −1 . The reported agreement of the theoretical spectrum and dissociation energy with experiment is contingent upon the inclusion of the effects of core-generated electron correlation, spin-orbit coupling, and scalar relativity. The Dunham analysis ͓Phys. Rev. 41, 721 ͑1932͔͒ of the spectrum is found to be very accurate. New values are given for the spectroscopic constants.

show abstract

Exploring the effect of anharmonicity of molecular vibrations on thermodynamic properties

Cited by 120 publications

References 66 publications

Predicting accurate vibrational frequencies for highly anharmonic systems

Predicting accurate vibrational frequencies for highly anharmonic systems

Ab Initio Calculation of Rate Constants for Molecule–Surface Reactions with Chemical Accuracy

Accurate ab initio potential energy curve of F2. III. The vibration rotation spectrum

Contact Info

Product

Resources

About