pbqff: Push-Button Quartic Force Fields

Westbrook, Brent R.; Fortenberry, Ryan C.

doi:10.1021/acs.jctc.3c00129

Cited by 24 publications

(16 citation statements)

References 48 publications

(80 reference statements)

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“…The resulting QFF utilizing coupled cluster harmonic terms and DFT anharmonic terms is then fed into a second-order vibrational perturbation theory (VPT2) code called pbQFF written in the modern Rust programming language built upon the previous Fortran77 Spectro code. , This produces the anharmonic fundamental vibrational frequencies and the rotational constants utilized for comparison to the experimental benchmarks: NH 2 – , HNO, HOO, HNF, HSO, HSS, H 2 CO, HOCO + , and formic acid. The HNO, HOO, HNF, HSO, and HSS F12-TcCR + EOM excited-state harmonic force constants are from ref .…”

Section: Methodsmentioning

confidence: 99%

DFT + F12 QFFs for Cost-Effective Rovibrational Spectral Data Predictions of Ground and Excited Electronic States

Garrett,

Davis,

Fortenberry

2024

J. Chem. Theory Comput.

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The quest for faster computation of anharmonic vibrational frequencies of both ground and excited electronic states has led to combining coupled cluster theory harmonic force constants with density functional theory cubic and quartic force constants for defining a quartic force field (QFF) utilized in conjunction with vibrational perturbation theory at second order (VPT2). This work shows that explicitly correlated coupled cluster theory at the singles, doubles, and perturbative triples levels [CCSD(T)-F12] provides accurate anharmonic vibrational frequencies and rotational constants when conjoined with any of B3LYP, CAM-B3LYP, BHandHLYP, PBE0, and ωB97XD for roughly one-quarter of the computational time of the CCSD(T)-F12 QFF alone for our test set. As the number of atoms in the molecule increases, however, the anharmonic terms become a greater portion of the QFF, and the cost comparison improves with HOCO+ and formic acid, requiring less than 15 and 10% of the time, respectively. In electronically excited states, PBE0 produces more consistently accurate results. Additionally, as the size of the molecule and, in turn, QFF increase, the cost savings for utilizing such a hybrid approach for both ground- and excited-state computations grows. As such, these methods are promising for predicting accurate rovibrational spectral properties for electronically excited states. In cases where well-behaved potentials for a small selection of targeted excited states are needed, such an approach should reduce the computational cost compared to that of methods requiring semiglobal potential surfaces or variational treatments of the rovibronic Hamiltonian. Such applications include spectral characterization of comets, exoplanets, or any situation in which gas phase molecules are being excited by UV–vis radiation.

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Section: Methodsmentioning

confidence: 99%

DFT + F12 QFFs for Cost-Effective Rovibrational Spectral Data Predictions of Ground and Excited Electronic States

Garrett,

Davis,

Fortenberry

2024

J. Chem. Theory Comput.

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“…F12-TZ has been shown to produce accurate fundamental vibrational frequencies and rotational constants at far less computational cost compared to other QFF methods (Martin & Kesharwani 2014;Inostroza-Pino et al 2020;Palmer & Fortenberry 2022). Additionally, the QFF implemented in this work is conducted within the recently developed automated PBQFF framework (Westbrook & Fortenberry 2023). The PBQFF procedure begins with a geometry optimzation utilizing MOLPRO (Werner et al 2020) at the F12-TZ level of theory with tight convergence criteria.…”

Section: Rovibrational Spectroscopic Methodsmentioning

confidence: 99%

Reaction Pathway and Rovibrational Analysis of Aluminum Nitride Species as Potential Dust Grain Nucleation Agents

Palmer,

Fortenberry

2024

ApJ

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A dust nucleating agent may be present in interstellar or circumstellar media that has gone seemingly undetected and unstudied for decades. Some analyses of the Murchison CM2 meteorite suggest that at least some of the aluminum present within condensed as aluminum nitrides instead of the long-studied, but heretofore undetected suite of aluminum oxides. The present theoretical study utilizes explicitly correlated coupled cluster theory and density functional theory to provide a formation pathway from alane (AlH3) and ammonia to the cyclic structure Al2N2H4, which has the proper Al/N ratio expected of bulk aluminum nitrides. Novel rovibrational spectroscopic constants are computed for alane and the first two formed structures, AlNH6 and AlNH4, along the reaction pathway for use as reference in possible laboratory or observational studies. The ν 8 bending frequency for AlNH6 at 755.7 cm−1 (13.23 μm) presents a vibrational transition intensity of 515 km mol−1, more intense than the antisymmetric C−O stretch of carbon dioxide, and contains a dipole moment of 5.40 D, which is ∼3× larger than that of water. Thus, the present reaction pathway and rovibrational spectroscopic analysis may potentially assist in the astrophysical detection of novel, inorganic species which may be indicative of larger dust grain nucleation.

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“…A refit to this function's minimum zeroes the gradients and produces the equilibrium geometry and corresponding force constants. These are then transformed from SICs into Cartesian coordinates using the INTDER program [127,128]. The Cartesian force constants are then used in second-order rotational and vibrational perturbation theory [23,129,130] within the SPECTRO software package [131] to calculate the rovibrational spectral data.…”

Section: Computational Detailsmentioning

confidence: 99%

“…Furthermore, the SPECTRO program has the ability to treat the above-define Fermi resonance polyads. As such, the present computations make use of this workflow of separate programs for the anharmonic computations, but the hybrid approach is also available in a streamlined, user-friendly fashion via the PBQFF code [128].…”

Section: Computational Detailsmentioning

confidence: 99%

The performance of hybrid and F12∗/F12c explicitly correlated coupled cluster methods for use in anharmonic vibrational frequency computations

Watrous,

Westbrook,

Fortenberry

2023

Int J of Quantum Chemistry

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A hybrid quartic force field approach produces the same accuracies as non‐hybrid methods but for less than one quarter of the computational time. This method utilizes explicitly correlated coupled cluster theory at the singles and doubles level inclusive of perturbative triples (CCSD(T)‐F12b) in conjunction with a triple‐ basis set, core electron correlation, and scalar relativity for the harmonic terms and CCSD(T)‐F12b with a valence double‐ basis set for the cubic and quartic terms. There is no sacrifice in the prediction of fundamental anharmonic vibrational frequencies or vibrationally‐averaged rotational constants as compared to experiment, but the time saved is notable. Other hybrid methods are examined involving different sizes of basis sets and composite terms included or excluded. Not one is more accurate; only one is faster. F12 (also called F12c) is tested as well, but it has an increase in computational time for no increase in accuracy. As such, this work reports a hybrid and composite approach (F12‐TcCR+DZ) in the computation of rovibrational spectral data which can be applied to the observation of novel molecules in the gas phase in the laboratory and potentially even in astrophysical environments.

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pbqff: Push-Button Quartic Force Fields

Cited by 24 publications

References 48 publications

DFT + F12 QFFs for Cost-Effective Rovibrational Spectral Data Predictions of Ground and Excited Electronic States

DFT + F12 QFFs for Cost-Effective Rovibrational Spectral Data Predictions of Ground and Excited Electronic States

Reaction Pathway and Rovibrational Analysis of Aluminum Nitride Species as Potential Dust Grain Nucleation Agents

The performance of hybrid and F12∗/F12c explicitly correlated coupled cluster methods for use in anharmonic vibrational frequency computations

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