(T)+EOM Quartic Force Fields for Theoretical Vibrational Spectroscopy of Electronically Excited States

Davis, Megan C.; Fortenberry, Ryan C.

doi:10.1021/acs.jctc.1c00307

Cited by 6 publications

(23 citation statements)

References 67 publications

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“…For electronically excited states, (T)+EOM/CcCR QFFs [ 39 ] are constructed by approximating the energy of a target higher electronic state as a combination of a ground-state CCSD(T) energy and an EOM-CCSD excitation energy to the target state. These (T)+EOM energies are used with the same core correlation and scalar relativistic corrections as in the ground state CcCR QFF to form the (T)+EOM/CcCR approach.…”

Section: Methodsmentioning

confidence: 99%

“…Additionally, providing theoretical data for low intensity vibrational frequencies would assist in thermodynamic characterization of these species and complete spectral modeling as would be required for the classification of cometary observations. Herein, a simple, but highly accurate [ 39 ] adiabatic approach is utilized in an attempt to provide fundamental vibrational frequencies for the electronically excited states for CO

, H

and H

.…”

Section: Introductionmentioning

confidence: 99%

“…Quartic force fields (QFFs) can be used readily and accurately to characterize vibrational frequencies, rotational constants, and other spectroscopic parameters for molecules in their ground electronic states [ 40 ]. These have previously been extended to electronically excited states [ 41 , 42 ] using EOM-CC3 [ 43 , 44 ] as well as the recently proposed (T)+EOM approach [ 39 ]. The last method has achieved mean absolute differences as low as 1.6 cm

for anharmonic frequencies relative to the established benchmark CcCR [ 45 ] approach (defined below).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations

2023

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New high-level ab initio quartic force field (QFF) methods are explored which provide spectroscopic data for the electronically excited states of the carbon monoxide, water, and formaldehyde cations, sentinel species for expanded, recent cometary spectral analysis. QFFs based on equation-of-motion ionization potential (EOM-IP) with a complete basis set extrapolation and core correlation corrections provide assignment for the fundamental vibrational frequencies of the Ã 2B1 and B̃ 2A1 states of the formaldehyde cation; only three of these frequencies have experimental assignment available. Rotational constants corresponding to these vibrational excitations are also provided for the first time for all electronically excited states of both of these molecules. EOM-IP-CCSDT/CcC computations support tentative re-assignment of the ν1 and ν3 frequencies of the B̃ 2B2 state of the water cation to approximately 2409.3 cm−1 and 1785.7 cm−1, respectively, due to significant disagreement between experimental assignment and all levels of theory computed herein, as well as work by previous authors. The EOM-IP-CCSDT/CcC QFF achieves agreement to within 12 cm−1 for the fundamental vibrational frequencies of the electronic ground state of the water cation compared to experimental values and to the high-level theoretical benchmarks for variationally-accessible states. Less costly EOM-IP based approaches are also explored using approximate triples coupled cluster methods, as well as electronically excited state QFFs based on EOM-CC3 and the previous (T)+EOM approach. The novel data, including vibrationally corrected rotational constants for all states studied herein, provided by these computations should be useful in clarifying comet evolution or other remote sensing applications in addition to fundamental spectroscopy.

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Section: Methodsmentioning

confidence: 99%

, H

and H

.…”

Section: Introductionmentioning

confidence: 99%

for anharmonic frequencies relative to the established benchmark CcCR [ 45 ] approach (defined below).…”

Section: Introductionmentioning

confidence: 99%

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Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations

2023

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“…The so-called (T)+EOM QFFs achieve accuracy compared to ground electronic state type benchmarks for a small set of triatomic test caseswithin 1.6 cm –1 for one speciesand thus seem to be a promising avenue of exploration. A (T)+EOM QFF accounts for some triples correction by approximating the total energy of the target state as a sum of a ground state CCSD(T) reference energy and an EOM-CCSD excitation energy from the reference state to the target electronic state of interest.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, in order to build upon the work presented in ref by developing a similar methodology with reduced cost, the present work shall herein define and test ”F12+EOM” QFFse.g., electronically excited state QFFs which utilize reference-state CCSD(T)-F12 energies with EOM-CCSD excitations to a target state. Ground state QFFs based purely on CCSD(T)-F12 energies without further corrections are accurate for vibrational frequencies but do not quite achieve spectroscopic accuracy for rotational constants .…”

Section: Introductionmentioning

confidence: 99%

F12+EOM Quartic Force Fields for Rovibrational Predictions of Electronically Excited States

2023

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Quartic force fields (QFFs) constructed using a sum of ground-state CCSD(T)-F12b energies with EOM-CCSD excitation energies are proposed for computation of spectroscopic properties of electronically excited states. This is dubbed the F12+EOM approach and is shown to provide similar accuracy to previous methodologies at lower computational cost. Using explicitly correlated F12 approaches instead of canonical CCSD(T), as in the corresponding (T)+EOM approach, allows for 70-fold improvement in computational time. The mean percent difference between the two methods for anharmonic vibrational frequencies is only 0.10%. A similar approach is also developed herein which accounts for core correlation and scalar relativistic effects, named F12cCR+EOM. The F12+EOM and F12cCR+EOM approaches both match to within 2.5% mean absolute error of experimental fundamental frequencies. These new methods should help in clarifying astronomical spectra by assigning features to vibronic and vibrational transitions of small astromolecules when such data are not available experimentally.

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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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(T)+EOM Quartic Force Fields for Theoretical Vibrational Spectroscopy of Electronically Excited States

Cited by 6 publications

References 67 publications

Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations

Complete, Theoretical Rovibronic Spectral Characterization of the Carbon Monoxide, Water, and Formaldehyde Cations

F12+EOM Quartic Force Fields for Rovibrational Predictions of Electronically Excited States

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

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