Assignment of normal modes for imidazole on the basis of 3-21G and 4-21G Ab Initio Force Fields

Based on cluster model, we have calculated the fundamental vibrational frequencies of rutile by combining ab initio method and Wilson’s GF-matrix method. In the calculation, we have introduced the concept of environment factor α to correct the force field of the cluster model. The results of calculation are in good agreement to the experimental data and the normal modes give us clear physical picture of the crystal vibration.

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In search of the next Holy Grail of polyoxide chemistry: Explicitly correlated ab initio full quartic force fields for HOOH, HOOOH, HOOOOH, and their isotopologues

The Journal of Chemical Physics ◽

10.1063/1.3684231 ◽

2012 ◽

Vol 136 (8) ◽

pp. 084302 ◽

Cited By ~ 24

Author(s):

David S. Hollman ◽

Henry F. Schaefer

Keyword(s):

Ab Initio ◽

Force Fields ◽

Holy Grail ◽

Explicitly Correlated

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Quantum-Chemical Ab Initio Calculations on Inda- and Thallabenzene (C5H5In and C5H5Tl) and their Structural Isomers η5-C5H5In and η5-C5H5Tl

Australian Journal of Chemistry ◽

10.1071/ch17472 ◽

2018 ◽

Vol 71 (3) ◽

pp. 102

Author(s):

Emma Persoon ◽

Yuekui Wang ◽

Gerhard Raabe

Keyword(s):

Ab Initio ◽

Quantum Chemical ◽

Density Functional ◽

Single Point ◽

Normal Modes ◽

Dft Method ◽

Basis Sets ◽

Triplet States ◽

Structural Isomers ◽

Td Dft

Quantum-chemical ab initio, time-independent, as well as time-dependent density functional theory (TD-DFT) calculations were performed on the so far elusive heterocycles inda- and thallabenzene (C5H5In and C5H5Tl), employing several different methods (MP2, CISD, CCSD, CCSD(T), BD, BD(T), QCISD, QCISD(T), CASSCF, DFT/B3LYP), effective core potentials, and different basis sets. While calculations on the MP2 level predict the ground states of the title compounds to be singlets with the first triplet states between 13 and 15 kcal mol−1 higher in energy, single point calculations with the QCISD(T), CCSD(T), and BD(T) methods at CCSD-optimized structures result in energy differences between the singlet and the triplet states in the range between 0.3 and 2.1 kcal mol−1 in favour of the triplet states. According to a CASSCF(8,8) calculation the triplets are also more stable by about 2.5–2.9 kcal mol−1. Calculations were also performed for the C5v-symmetric η5 structural isomers (cyclopentadienylindium, CpIn, and cyclopentadienylthallium, CpTl, Cp = C5H5) of the title compounds. At the highest level of theory employed in this study, C5H5In is between 79 and 88 kcal mol−1 higher in energy than CpIn, while this energy difference is even larger for thallabenzene where C5H5Tl is energetically between 94 and 102 kcal mol−1 above CpTl. In addition we report on the UV/vis spectra calculated with a TD-DFT method as well as on the spectra of the normal modes of C5H5In and C5H5Tl. Both types of spectra might facilitate identification of the title compounds eventually formed in photolysis or pyrolysis experiments.

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High-level ab initio quartic force fields and spectroscopic characterization of C2N−

Physical Chemistry Chemical Physics ◽

10.1039/d1cp03505c ◽

2021 ◽

Author(s):

Carlos M. Rocha ◽

H V J Linnartz

Keyword(s):

Ab Initio ◽

Force Fields ◽

Electron Attachment ◽

Spectroscopic Characterization ◽

Carbon Chain ◽

Molecular Anions ◽

High Level

While it is now well established that large carbon chain species and radiative electron attachment (REA) are key ingredients triggering interstellar anion chemistry, the role played by smaller molecular anions,...

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Empirical Potential-Energy Surfaces Fitting Using Feed forward Neural Networks

Neural Networks in Chemical Reaction Dynamics ◽

10.1093/oso/9780199765652.003.0012 ◽

2012 ◽

Author(s):

Lionel Raff ◽

Ranga Komanduri ◽

Martin Hagan ◽

Satish Bukkapatnam

Keyword(s):

Potential Energy ◽

Ab Initio ◽

Potential Energy Surfaces ◽

Force Fields ◽

Pair Potential ◽

Potential Surfaces ◽

Empirical Potential ◽

Functional Forms ◽

Dynamics Simulations ◽

Energy Surfaces

When the system of interest becomes too complex to permit the use of ab initio methods to obtain the system potential-energy surfaces (PES), empirical potential surfaces are frequently employed to represent the force fields present in the system under investigation. In most cases, the functional forms present in these potentials are selected on the basis of chemical and physical intuitions. The parameters of the surface are frequently adjusted to fit a very small set of experimental data that comprise bond energies, equilibrium bond distances and angles, fundamental vibrational frequencies, and perhaps measured barrier heights to reactions of interest. Such potentials generally yield only qualitative or semiquantitative descriptions of the system dynamics. Several research groups have significantly improved the accuracy of the values of the experimental properties computed using empirical potential surfaces by fitting the chosen functional form for the potential to the force fields obtained from trajectories using ab initio Car-Parrinello molecular dynamics simulations. The fitting to the force fields is usually done using a least-squares fitting approach. This method has been employed by Izvekov et al. to obtain effective non-polarizable three-site force fields for liquid water. Carré et al. have employed such a procedure to obtain a new pair potential for silica. In their investigation, the vector of potential parameters was fitted using an iterative Levenberg-Marquardt algorithm. Tangney and Scandolo have also developed an interatomic force field for liquid SiO2 in which the parameters were fitted to the forces, stresses, and energies obtained from ab initio calculations. Ercolessi and Adams have used a quasi-Newtonian procedure to fit an empirical potential for aluminum to data obtained from first-principals computations. Empirical potentials can be improved by making the parameters parameterized functions of the coordinates defining the instantaneous positions of the atoms of the system. This approach has been successfully employed by numerous investigators The difficulty with this procedure is that the number of parameters that must be adjusted increases rapidly. Appropriate fitting of these parameters requires a much more extensive database. Finally, the actual fitting process can often be tedious, difficult, and time-consuming.

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