Direct fit of extended Hartree–Fock approximate correlation energy model to spectroscopic data

Varandas, A. J. C.; Rodrigues, Sérgio Paulo Jorge; Batista, V.

doi:10.1016/j.cplett.2006.04.084

Cited by 21 publications

(14 citation statements)

References 28 publications

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“…In summary, we judge the fit of the present work as quite satisfactory particularly because it does not involve any fitting to the observed vibrational data. Moreover, it may provide the required input for later improvement to true spectroscopy accuracy either via a direct fit 114,133,134 to spectroscopic data or by morphing the current PES with a spectroscopically accurate local potential via energy-switching. 112,135,136 …”

mentioning

confidence: 99%

Accurate ab initio-based double many-body expansion potential energy surface for the adiabatic ground-state of the C3 radical including combined Jahn-Teller plus pseudo-Jahn-Teller interactions

Rocha

Varandas

2015

The Journal of Chemical Physics

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A fully ab initio-based potential energy surface is first reported for the ground electronic state of the C3 radical using the double many-body expansion (DMBE) method. The DMBE form so obtained mimics the full set of energies calculated at the multireference configuration interaction level of theory with chemical accuracy. To account for the incompleteness of the one- and N-electron bases, the calculated external correlation energies have been scaled prior to the fitting procedure via DMBE-scaled external correlation method. Furthermore, the novel potential energy surface reproduces accurately dissociation energies, diatomic potentials, long-range interactions at all asymptotic channels, and the correct topological behavior at the region of 4 conical intersections with the partner state of the same symmetry near equilateral triangular geometries due to combined Jahn-Teller (E' ⊗ e') plus pseudo-Jahn-Teller [(E'+A1')⊗e'] interactions. Rovibrational calculations have also been performed, unveiling a good match of the vibrational spectrum of C3 for 53 calculated levels. The present DMBE form is, therefore, commended for both spectroscopic and reaction dynamics studies, some also performed in the present work.

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mentioning

confidence: 99%

Accurate ab initio-based double many-body expansion potential energy surface for the adiabatic ground-state of the C3 radical including combined Jahn-Teller plus pseudo-Jahn-Teller interactions

Rocha

Varandas

2015

The Journal of Chemical Physics

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“…Besides, we should have in mind that only the first 23 vibrational levels have been counted for the statistics. We recall that a direct least-squares fit [25] to 90 ro-vibrational spectroscopic term values [26] and the 23 RKR points reported by Krupenie [24], let to an O 2 potential that reproduces the input data with a rmsd of 0.6 cm À1 for the 90 ro-vibrational energies (1.4 cm À1 with respect to the 18 vibrational energies), and 22 cm À1 for the RKR points. Somewhat coincidentally, perhaps, we obtain a rmsd of similar order of magnitude from our CS N /USTE(T, Q) curves.…”

Section: Resultsmentioning

confidence: 99%

Accurate global ab initio potentials at low-cost by correlation scaling and extrapolation to the one-electron basis set limit

Varandas

2007

Chemical Physics Letters

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A recently proposed scheme that enables a potential energy surface corresponding to a calculation with a large target basis set to be obtained from small basis set calculations via scaling of the electron correlation at a single-pivotal geometry is generalized to include an arbitrary number of such geometries. If the correlation is extrapolated to the complete basis set limit at the pivotal geometries and used for the scaling, the method can yield accurate potentials at costs up to factors nearly fifty times cheaper than required otherwise. The approach, free from parameters alien to the ab initio methods, is tested on N 2 , O 2 , and F 2 .

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“…In the work of CH1, the long‐range portion of the PEF included only the leading dispersion coefficient, C 6 . In the present work, two successive dispersion energy coefficients, C 8 and C 10 , were estimated employing the formula,

C_{n} = C_{6} κ_{n} R_{0}^{1.57 (n - 6) / 2},

where κ 8 = 1.00, κ 10 = 1.13, and R 0 is the Le Roy radius. The Le Roy radius for the ground electronic state of HI is R 0 = 4.53 Å, and C 6 = 2.28 × 10 5 Å 6 cm −1 , taken from CH1.…”

Section: Applications and Discussionmentioning

confidence: 99%

The extended Hulburt–Hirschfelder‐long‐range oscillator model for direct‐potential‐fit analysis

Hajigeorgiou

2017

Int J of Quantum Chemistry

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In the present work, an extended Hulburt-Hirschfelder oscillator model is proposed as a means of simplifying potential energy functions for direct-potential-fit analyses. The new potential energy function is joined smoothly to the long-range inverse-power dispersion energy expression. The new model is employed in direct-potential-fits using spectroscopic line positions that involve the ground electronic states of the principal isotopologues of hydrogen iodide and carbon monoxide, and the ground and first singlet-sigma excited states of hydrogen fluoride and hydrogen chloride.The present methodology is found to lead to compact, flexible, and robust representations for the potential energy that compare favorably with the results of past work where more complicated models were employed.analytical diatomic potential, CO, direct-potential-fit, extended Hulburt-Hirschfelder oscillator, HCl , HF, HI | I N TR ODU C TI ONThe determination of a potential energy function (PEF) for diatomic molecules from analysis of spectroscopic line positions is a very important objective in molecular physics. A PEF in compact analytical form is a most economical means of summarizing the quantum-mechanical vibrationalrotational energy level manifold for diatomic systems. A principal advantage of a PEF over traditional molecular constants is the considerably more reliable extrapolation to experimentally unobserved energy levels. Moreover, the radial eigenfunctions of the PEF that can be readily supplied through numerical solution of the Schr€ odinger equation can be employed to estimate transition probabilities, when in conjunction with an electric dipole moment function. The concept of a PEF for nuclear motion is supported theoretically by the Born-Oppenheimer approximation, [1] widely recognized as one of the cornerstones of chemical physics. Two fundamental parameters of the diatomic PEF are the equilibrium internuclear separation, or the distance where the potential energy reaches a minimum value, and the dissociation energy, which is the energy required in separating the two constituent atoms. The radial dependence of a PEF describes the behavior of a chemical bond, one of the most highly treasured concepts in chemistry.Modern methods of determining the PEF from spectroscopic information have been reviewed by Le Roy. [2] Of particular interest are directpotential-fit (DPF) methods, whereby the PEF is represented by a flexible multiparameter analytical model that is quantum-mechanically consistent with the spectroscopic information employed in its estimation. The pleasing result is that the vibrational-rotational point spectrum obtained by numerical solution of the radial Schr€ odinger equation, reproduces the experimental spectroscopic transition energies to within the associated measurement uncertainties, on average. Mathematical models employed in representing the PEF for DPF analyses vary in degree of sophistication; a useful summary of the evolution of such functions has been provided recently by Hajigeorgiou. [3] The most success...

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Direct fit of extended Hartree–Fock approximate correlation energy model to spectroscopic data

Cited by 21 publications

References 28 publications

Accurate ab initio-based double many-body expansion potential energy surface for the adiabatic ground-state of the C3 radical including combined Jahn-Teller plus pseudo-Jahn-Teller interactions

Accurate ab initio-based double many-body expansion potential energy surface for the adiabatic ground-state of the C3 radical including combined Jahn-Teller plus pseudo-Jahn-Teller interactions

Accurate global ab initio potentials at low-cost by correlation scaling and extrapolation to the one-electron basis set limit

The extended Hulburt–Hirschfelder‐long‐range oscillator model for direct‐potential‐fit analysis

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