Theoretical enthalpies of formation of large compounds using integrated methods

Espinosa‐García, J.; García-Bernáldez, J. C.

doi:10.1039/b202671f

Cited by 44 publications

(85 citation statements)

References 45 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…H 2 1CH 3 reaction are shown. Results from MCTDH [7] and RPMD [126] calculations are shown as well as results from canonical variational transition state theory with microcanonically optimized multidimensional tunneling [7,8] and classical transition state theory (TST). [126] The potential energy surface that has been used to calculate all rate constants in the table is due to Espinosa-Garcia.…”

Section: I5mentioning

confidence: 99%

“…[126] The potential energy surface that has been used to calculate all rate constants in the table is due to Espinosa-Garcia. [8] The rate constants from the MCTDH calculations are considered to be the most accurate ones, against which the others can be compared. It is estimated that the MCTDH calculations are converged to within about 10%, meaning that the MCTDH calculated rate constants should be within 10% of the exact values for the given potential energy surface.…”

Section: I5mentioning

confidence: 99%

“…Calculated thermal rate constants for the H1CH 4 fiH 2 1CH 3 reaction on the PJEG potential energy surface [8] obtained using MCTDH, [7] , RPMD, [126] , canonical variational transition state theory with microcanonically optimized multi-dimensional tunneling [7,8] and classical transition state theory. [126] The rate constants are given in cm 3 /mol/s and the numbers in parenthesis denote powers of 10.…”

Section: Summary and Concluding Remarksmentioning

confidence: 99%

“…This is primarily due to the facts that it is a light atom (hydrogen) that is involved in the bond breaking and bond forming and that there is a substantial barrier to reaction, the height of which is 12.9 kcal/mol on the potential energy surface that was used. [8] Note also that the barrier height is not the sole factor determining the rate constant, also the shape of the barrier makes a difference as soon as tunneling matters.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Computational methods of quantum reaction dynamics

Nyman

2014

Int J of Quantum Chemistry

View full text Add to dashboard Cite

In this article, I review some of the best available quantum dynamical approaches for studying bimolecular chemical reactions. Calculating the thermal rate constant is central in theoretical chemistry and there is a focus on this. I begin by motivating the need for quantum dynamics before giving a general overview. Thereafter, I give expressions for calculating thermal rate constants. This is followed by a brief description of time-independent scattering calculations.Next comes a longer section on time-dependent approaches including the time-dependent wave packet approach, the multiconfigurational time-dependent Hartree approach and ring polymer molecular dynamics. Finally, I make some concluding remarks.

show abstract

Section: I5mentioning

confidence: 99%

Section: I5mentioning

confidence: 99%

Section: Summary and Concluding Remarksmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Computational methods of quantum reaction dynamics

Nyman

2014

Int J of Quantum Chemistry

View full text Add to dashboard Cite

show abstract

“…The ONIOM method application in thermochemical studies have been done considering various chemical species. [49][50][51] The link between the ONIOM and the composite methods allows the calculation of systems with many atoms at high level theory. Both methodologies use the extrapolation of their energies to more accurate results.…”

mentioning

confidence: 99%

Theoretical study of thermochemical properties using composite methods adapted to ONIOM

Heerdt

Morgon

2012

J. Braz. Chem. Soc.

View full text Add to dashboard Cite

Métodos compostos adaptados ao método ONIOM foram utilizados no cálculo teórico de afinidades por próton (PA) e eletrônica (EA) para um grupo de 50 moléculas (álcoois, cetonas, radicais e alcenos). A energia eletrônica foi descrita considerando-se o escalonamento de ZPE (λ) e a correção de alto nível (HLC). O valor ótimo para λ foi obtido através dos dados de PA. Os cálculos de EA foram utilizados na otimização dos termos presentes em HLC. Foram explorados diferentes tipos de funcionais de troca-correlação. A metodologia ONIOM2(QCISD(T)/6-311++G(2dF,p):HF/6-31G(d))//ONIOM2(B3LYP/6-31G(d):HF/6-31G(d)) forneceu os menores desvios absolutos médios para PA e EA, 5,38 kJ mol -1 e 0,11 eV, respectivamente, em comparação com dados experimentais.Composite methods adapted to the ONIOM approach were used in the description of proton (PA) and electron (EA) affinities for a group of 50 molecules (alcohols, ketones, radicals and alkenes). The electronic energy was described considering the scaling ZPE (λ) and higher level (HLC) corrections. The optimal value for λ was obtained from the PA data. The EA calculations were used for optimization of the terms in HLC. Different performances of exchange-correlation functionals were considered. The methodology ONIOM2(QCISD(T)/6-311++G(2dF,p):HF/6-31G(d))//ONIOM2(B3LYP/6-31G(d):HF/6-31G(d)) provided the smallest median absolute deviation (MAD) for PA and EA, 5.38 kJ mol -1 and 0.11 eV, respectively, in comparison to the experimental data.Keywords: proton and electron affinities, composite methods, ONIOM Introduction Molecular modeling calculations using high level (ab initio and DFT methods) and large basis sets have provided determinations of the precise electronic properties of atomic and molecular systems. 1-9 However, practical calculations containing many particles become a task that requires a very high computational cost. 10 Some strategies have been successful, making it possible to study large systems, highlighting the composite methods [11][12][13][14][15][16][17][18][19] and the ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) method. 20 Developed in the 1980s, the composite methods aim to extrapolate the electronic energies from a sequence of calculations, computationally inexpensive, to an electronic energy with a high level of correlation and large basis set. 2 In addition to the energy terms from the energy calculations, some empirical parameters can be added to correct deficiencies of the method, like additional correlation effects, relativistic effect, etc.The Gaussian-n theory, developed by Pople and co-workers, 13-17 exploits this idea to predict thermochemical data of molecules containing elements of the first three periods of the periodic table. The purpose of this theory is to obtain a general procedure that can reproduce experimental data for properties such as proton and electron affinities, ionization energy, enthalpy of formation, etc., being applicable to any molecular system unambiguously. Recently, new approaches of these theo...

show abstract

Dynamics of the Simplest Reaction of a Carbon Atom in a Tetrahedral Environment

2003

View full text Add to dashboard Cite

Reactions occurring at a carbon center are one of the most important and useful classes of reactions in chemistry. The simplest reaction at a carbon atom with a tetrahedral environment is that of an H atom with methane, and understanding this prototypical reaction has implications for a number of fields ranging from organic and combustion chemistry to fundamental reaction dynamics. Consequently, it has been the subject of numerous experimental studies [1] exploring the kinetics and isotope effects of both the forward and reverse reactions. Recent theoretical work includes new potential energy surface calculations, [2][3][4][5][6] direct dynamics studies, [7] calculation of isotope effects, [8] and new quantum scattering methods [9] that have been reviewed by Althorpe and Clary.[10]Herein we report the first study of the nascent CD 3 products from the H + CD 4 reaction. This isotope combination was chosen for experimental reasons because this arrangement allows for the detection of all possible reaction products: CD 3 , HD and D. We also examined the CH 3 products from the H + CH 4 reaction and find that it shows very similar behavior [11] to that reported herein for the H + CD 4 reaction. By using the well-established photoloc technique, [12] we find that at a collision energy of 1.95 AE 0.05 eV the CD 3 products are produced in their ground vibrational state or have one quantum of excitation in the low-frequency umbrella-bending mode (n 2 ). In addition, the CD 3 products are sideways/backward scattered [hcos qi = À0.20 AE 0.09] with respect to the incident H-atom direction. This result stands in stark contrast with the benchmark H + D 2 !HD + D bimolecular exchange reaction in which the D atom is scattered in the same direction as the incoming H atom, thus indicating a rebound mechanism.[13] The H + D 2 reaction is a logical choice for comparison with the H + CD 4 abstraction reaction because they are both nearly thermoneutral and have similar classical barriers. [14,15] We propose two possible explanations for the unusual angular distribution of the CD 3 products: (1) a stripping mechanism is more important at this energy than a rebound mechanism, and (2) a competition between abstraction and exchange diminishes the probability for abstraction at small impact parameters.Hot-atom chemistry has established the existence of the abstraction and exchange channels by using T atoms from nuclear recoil experiments [16] and photolytic sources.[17] Equation (1) and Equation (2) are close to thermoneutralbut have very different classical barrier heights (0.65 and 1.65 eV respectively). [14] Since the early hot-atom studies, experimental probes of the dynamics have been rather sparse. Valentini and coworkers [18] examined the abstraction channel by measuring the rovibrational state distributions of the HD product from H + CD 4 at 1.5 eV by using coherent antiStokes Raman spectroscopy (CARS). They found that the total cross section for reaction is 0.14 AE 0.03 2 , from which it is concluded that the maximum impact paramete...

show abstract

Theoretical enthalpies of formation of large compounds using integrated methods

Cited by 44 publications

References 45 publications

Computational methods of quantum reaction dynamics

Computational methods of quantum reaction dynamics

Theoretical study of thermochemical properties using composite methods adapted to ONIOM

Dynamics of the Simplest Reaction of a Carbon Atom in a Tetrahedral Environment

Contact Info

Product

Resources

About