An efficient algorithm for the determination of force constants and displacements in numerical definitions of a large, general order Taylor series expansion

Thackston, Russell; Fortenberry, Ryan C.

doi:10.1007/s10910-017-0783-3

Cited by 16 publications

(12 citation statements)

References 44 publications

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“…After the optimizations, each geometry is displaced by 0.005 Å or 0.005 radians to construct the QFFs . For each CcCR displacement, the total single-point energies are computed as combinations of the seven component energies shown below: where E CBS is the energy of the three-point TQ5 CBS extrapolation , given by in which A , B , and C are the energies from the 5Z, QZ, and TZ basis set computations, respectively, and l is the highest angular momentum function included in the basis set .…”

Section: Computational Detailsmentioning

confidence: 99%

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F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

2021

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The F12-TZ-cCR quartic force field (QFF) methodology, defined here as CCSD(T)-F12b/cc-pCVTZ-F12 with further corrections for relativity, is introduced as a cheaper and even more accurate alternative to more costly composite QFF methods like those containing complete basis set extrapolations within canonical coupled cluster theory. F12-TZ-cCR QFFs produce B 0 and C 0 vibrationally averaged principal rotational constants within 7.5 MHz of gas-phase experimental values for tetraatomic and larger molecules, offering higher accuracy in these constants than the previous composite methods. In addition, F12-TZ-cCR offers an order of magnitude decrease in the computational cost of highly accurate QFF methodologies accompanying this increase in accuracy. An additional order of magnitude in cost reduction is achieved in the F12-DZ-cCR method, while also matching the accuracy of the traditional composite method's B 0 and C 0 constants. Finally, F12-DZ and F12-TZ are benchmarked on the same test set, revealing that both methods can provide anharmonic vibrational frequencies that are comparable in accuracy to all three of the more expensive methodologies, although their rotational constants lag behind. Hence, the present work demonstrates that highly accurate theoretical rovibrational spectral data can be obtained for a fraction of the cost of conventional QFF methodologies, extending the applicability of QFFs to larger molecules.

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Section: Computational Detailsmentioning

confidence: 99%

“…46 After the optimizations, each geometry is displaced by 0.005 Å or 0.005 radians to construct the QFFs. 47 For each CcCR displacement, the total single-point energies are computed as combinations of the seven component energies shown below:…”

Section: ■ Computational Detailsmentioning

confidence: 99%

F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

2021

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“…Regardless of the method, the QFF is defined from 1585 points based on displacements of the reference geometry using the below S i symmetry-internal coordinates defined by Equ. 1-9 and an efficient lazy-Cartesian algorithm to construct the displacements (Thackston & Fortenberry 2018). The bond lengths are displaced by 0.005 Å and the angles as well as the in-plane (LINX) and out-of-plane (LINY) near-linear bends are displaced by 0.005 radians.…”

Section: Computational Detailsmentioning

confidence: 99%

The Fundamental Vibrational Frequencies and Spectroscopic Constants of the Dicyanoamine Anion, NCNCN⁻ (C₂N₃ ⁻): Quantum Chemical Analysis for Astrophysical and Planetary Environments

Dubois

Sciamma-O’Brien

Fortenberry

2019

ApJ

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Detecting anions in space has relied on a strong collaboration between theoretical and laboratory analyses to measure rotational spectra and spectroscopic constants to high accuracy. The advent of improved quantum chemical tools operating at higher accuracy and reduced computational cost is a crucial solution for the fundamental characterization of astrophysically-relevant anions and their detection in the interstellar medium and planetary atmospheres. In this context, we have turned towards the quantum chemical analysis of the pentaatomic dicyanoamine anion NCNCN − (C 2 N 3 − ), a structurally bent and polar compound. We have performed high-level coupled cluster theory quartic force field (QFF) computations of C 2 N 3 − satisfying both computational cost and accuracy conditions. We provide for the first time accurate spectroscopic constants and vibrational frequencies for this ion. In addition to exhibiting various Fermi resonances, C 2 N 3 − displays a bright ν 2 (2130.9 cm −1 ) and a less intense ν 1 (2190.7 cm −1 ) fundamental vibrational frequency, making for strong markers for future infrared observations < 5µm. We have also determined near-IR overtone and combination bands of the bright fundamentals for which the 2ν 2 at 4312.1 cm −1 (2.319 µm) is the best candidate. C 2 N 3 − could potentially exist and be detected in nitrogen-rich environments of the ISM such as IRC +10216 and other carbonrich circumstellar envelopes, or in the atmosphere of Saturn's moon Titan, where advanced N-based reactions may lead to its formation.

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“…The CCSD(T)-F12/cc-pVTZ-F12 geometry is first optimized, and then displacements of 0.005 Å and 0.005 radians, respective of bond stretches and bends/torsions, are produced for each of the nine internal coordinates. As a result of the C 1 point group of these molecules, the internal coordinates are the straightforward and standard bonds, angles, and dihedrals and are enumerated from the atom numbering in Figure as This requires 5641 total energy points to be computed to define the subsequent surface defined through a lazy-Cartesian algorithm . The surface is fit via a least squares procedure to define the true equilibrium geometry and then refit to produce the corresponding quadratic, cubic, and quartic force constants.…”

Section: Computational Detailsmentioning

confidence: 99%

“…This requires 5641 total energy points to be computed to define the subsequent surface defined through a lazy-Cartesian algorithm. 42 The surface is fit via a least squares procedure to define the true equilibrium geometry and then refit to produce the corresponding quadratic, cubic, and quartic force constants. These are transformed into Cartesian coordinates via the INTDER program 43 to make them generic for use in the SPECTRO program, 44 where second-order rotational 45 and vibrational perturbation theory (VPT2) 46,47 will produce the desired spectroscopic observables.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Rovibrational Characterization of CH₂ClH⁺, a Low-Energy Isomer of Ionized Chloromethane

Agbaglo

Fortenberry

2019

ACS Earth Space Chem.

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The astrophysical detection of chloromethane indicates that a low-energy form of the cation, the methyl chloronium cation (CH 2 ClH + ), may also be found in similar regions. Quantum chemical computations are providing what have been previously benchmarked as reliable vibrational frequencies and spectroscopic constants for this openshell cation. The ν 3 Cl−H stretch at 2630.5 cm −1 has a relatively large intensity and sits at 3.80 μm in a fairly unpopulated region of most astronomical infrared spectra, where it could more readily be distinguished from polycyclic aromatic hydrocarbons or other complex organic species. The 1.48 D center-of-mass computed dipole moment of CH 2 ClH + makes it observable rotationally, and its differences in structure and rotational constants from chloromethane will distinguish this cation isomer from its neutral counterpart. Such would have application for observational analysis with either groundbased radio telescopes or from the upcoming James Webb Space Telescope.

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An efficient algorithm for the determination of force constants and displacements in numerical definitions of a large, general order Taylor series expansion

Cited by 16 publications

References 44 publications

F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

The Fundamental Vibrational Frequencies and Spectroscopic Constants of the Dicyanoamine Anion, NCNCN⁻ (C₂N₃ ⁻): Quantum Chemical Analysis for Astrophysical and Planetary Environments

Quantum Chemical Rovibrational Characterization of CH₂ClH⁺, a Low-Energy Isomer of Ionized Chloromethane

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An efficient algorithm for the determination of force constants and displacements in numerical definitions of a large, general order Taylor series expansion

Cited by 16 publications

References 44 publications

F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

F12-TZ-cCR: A Methodology for Faster and Still Highly Accurate Quartic Force Fields

The Fundamental Vibrational Frequencies and Spectroscopic Constants of the Dicyanoamine Anion, NCNCN− (C2N3 −): Quantum Chemical Analysis for Astrophysical and Planetary Environments

Quantum Chemical Rovibrational Characterization of CH2ClH+, a Low-Energy Isomer of Ionized Chloromethane

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Product

Resources

About

The Fundamental Vibrational Frequencies and Spectroscopic Constants of the Dicyanoamine Anion, NCNCN⁻ (C₂N₃ ⁻): Quantum Chemical Analysis for Astrophysical and Planetary Environments

Quantum Chemical Rovibrational Characterization of CH₂ClH⁺, a Low-Energy Isomer of Ionized Chloromethane