The frozen orbital approximation for calculating ionization energies with application to propane

Müller, Wolfgang; Nager, Christoph; Rosmus, P.

doi:10.1016/0301-0104(80)80078-4

Cited by 6 publications

(2 citation statements)

References 32 publications

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“…On the other hand, in the Koopmans theorem, the frozen orbital approximation assumes that the N±1electron state (positive or negative ion) is equal to the N-electron state, neglecting the spin-orbital relaxation and producing overestimations in the IP values (Müller, 1980;Szabo and Ostluand, 1996;Plakhutin, 2018). The systematic errors mentioned above, Independent-Particle and frozen orbital approximations, cancel each other and generate good IP results.…”

Section: Discussionmentioning

confidence: 99%

Photon Harvesting Molecules: Ionization Potential from Quantum Chemical Calculations of Phytoplanktonic Pigments for MALDI-MS Analysis

Jaramillo¹,

Sánchez²,

Montañez³

et al. 2021

Orinoquia

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The Ionization Potential (IP) of chemical species is of paramount importance for the Matrix Assisted Laser Desorption/Ionization (MALDI) analyticaltechnique. Specifically, IPs are used in MALDI MS Electron Transfer (ET) as a parameter to select the matrix for a given family of chemical species. We useda quantum chemical methodology to computationally determine IPs for a set of photosensible phytoplanktonic pigments. These calculations could be used as a guide for MALDI matrix selection. IPs were determined using Koopman’s Theorem, via Geometry Optimization and Single Point Energy within the Restricted Closed-Shell Hartree-Fock (RHF) technique. Structures of a twenty-four set of pigments were geometrically optimized, and their IPsdetermined. Calculated IP’s are in close agreement to reported experimental IPs within an average 3.7% absolute error. Structural features of the chemical species studied have a closed relationship with their chemical properties and IP’s. Our results suggest that ET-MALDI matrices such as DCTB (IP = 8.5 eV) and CNPV-OCH3 (IP = 8.3 eV) could be more suitable to analyze these types of chemical species.

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Section: Discussionmentioning

confidence: 99%

Photon Harvesting Molecules: Ionization Potential from Quantum Chemical Calculations of Phytoplanktonic Pigments for MALDI-MS Analysis

Jaramillo¹,

Sánchez²,

Montañez³

et al. 2021

Orinoquia

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“…Not a rigorous but a very practical way to lower the computational effort of excited‐state calculations using high‐level correlation methods is the reduction of the virtual orbital space employed for the construction of the excited states . In general, the inner core orbitals can be excluded in the excitation energy calculation in most practical applications since they provide only a tiny contribution to differential electron correlations, and thus the frozen‐core approximation is a long‐known concept.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the restricted virtual space approximation in the algebraic‐diagrammatic construction scheme for the polarization propagator to speed‐up excited‐state calculations

Yang

Dreuw

2017

J Comput Chem

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The applicability and limitations of the restricted virtual space (RVS) approximation within the algebraic-diagrammatic construction (ADC) scheme for the polarization propagator up to third order is evaluated. In RVS-ADC, not only the core but also a substantial amount of energetically high-lying virtual orbitals is restricted in excitation energy calculations of low-lying excited electronic states. Using octatetraene, indole, and pyridine as representative examples and different standard basis sets of triple-zeta quality, RVS-ADC(2) turns out to be highly useful and to have negligible effects on ππ* excited states. However, for nπ* or πσ* states, the RVS approximation is generally less reliable but better at third-order than second-order ADC level. In addition, a unified, basis-set independent, thus normalized virtual orbital threshold (value) is introduced, making the RVS approximation more controllable and a priori applicable. © 2017 Wiley Periodicals, Inc.

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The Ionization of Alkanes

Bouma

Poppinger

Radom

1983

Israel Journal of Chemistry

100

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Ab initio molecular orbital theory has been used to study the ionization of methane, ethane, propane, n‐butane, isobutane, cyclopropane and cyclobutane. For methane radical cation, the preferred structure has C20 symmetry and a pair of long C—H bonds, resembling a complex of CH+2 with H2. This appears to be the only significant minimum on the CH+4 surface. For the remaining acyclic systems, the calculated structures of lowest energy (e.g., CH3‐CH2—CH+3, CH3‐CH2—CH2‐CH+3) are characterized by the extreme lengthening of a single C—C bond. However, alternative structures with two or more elongated C—C bonds have very low relative energies. The main structural conclusion for the alkane and cycloalkane radical cations is that the potential energy surface connecting various possible isomeric structures is generally very flat. Facile wide amplitude distortions and scrambling processes are therefore expected in these ions. The large structural changes which accompany ionization are manifested in large differences between vertical and adiabatic ionization potentials.

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The frozen orbital approximation for calculating ionization energies with application to propane

Cited by 6 publications

References 32 publications

Photon Harvesting Molecules: Ionization Potential from Quantum Chemical Calculations of Phytoplanktonic Pigments for MALDI-MS Analysis

Photon Harvesting Molecules: Ionization Potential from Quantum Chemical Calculations of Phytoplanktonic Pigments for MALDI-MS Analysis

Evaluation of the restricted virtual space approximation in the algebraic‐diagrammatic construction scheme for the polarization propagator to speed‐up excited‐state calculations

The Ionization of Alkanes

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