Analysis of the inadequacies of some semi‐empirical MO methods as theories of structure and reactivity

Bruijn, S. de

doi:10.1002/qua.560250209

Cited by 20 publications

(6 citation statements)

References 40 publications

(28 reference statements)

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“…Ions produced by doping the solid may also lead to perturbed chain excitations [52]. Orenstein and Baker [42], however, have observed a photogenerated intrinsic optical transition at -0.5 eV in transpolyacetylene and speculated that the feature may be due to radical cation absorption of the type considered here. Elucidation of the low-temperature optical spectrum is further complicated by the probable presence of the corresponding anions.…”

Section: E Extrapolation To Longer Linear Polyenesmentioning

confidence: 92%

“…The proposed adjustment simply compresses the divergence to the experimental-energy distribution based on best estimates from selected UPS studies. DeBruijn [42] further showed that such errors are not strongly manifest in the evaluation of excitations to the virtual levels. These scaling procedures have been applied to the study of the ionstate properties of additional systems with apparent success [20,37,43].…”

Section: Computationalmentioning

confidence: 97%

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Correlation contributions to the radical cation states of linear even polyenes: An open‐shell RHF‐CNDO/S(CI) analysis of the optical and photoelectron spectra

Bigelow

1986

Int J of Quantum Chemistry

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Configuration interaction wave functions are calculated for the low-lying radical cation states of transbutadiene, hexatriene, and octatetraene within the open-shell RHF-CNDOIS(CI) approach. The consequences of various one-electron contributions to the interpretation of existing photoemission and radical cation optical spectra are emphasized. Electron correlation is shown to be essential to achieve adequate energy and intensity profiles assuming photoelectron or optical excitation. The excitation energies and transition amplitudes (optical and photoemission) are also found to be sensitive to the molecular geometry. The present results are consistent with previous interpretations that photoionization measurements probe the neutralmolecule alternating single-double bond-length structure, whereas optical excitation samples an ion-statestate-induced "relaxed" reference configuration having a weakened bond-length alternation. Calculated wends in the spectroscopic properties are extrapolated to extended members of the even-polyene series.

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Section: E Extrapolation To Longer Linear Polyenesmentioning

confidence: 92%

Section: Computationalmentioning

confidence: 97%

Correlation contributions to the radical cation states of linear even polyenes: An open‐shell RHF‐CNDO/S(CI) analysis of the optical and photoelectron spectra

Bigelow

1986

Int J of Quantum Chemistry

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“…Apart from this example, it is evident that orthogonalization effects,

^{ϕ} H_{μν} = \sum_{λ = 1}^{M} \sum_{σ = 1}^{M} {((), ^{χ} S^{- \frac{1}{2}})}_{μ λ}^{}^{χ} H_{λσ} {(^{χ} S^{- \frac{1}{2}})}_{σν},

cannot be captured by introducing element‐dependent parameters which was, for instance, pointed out in Refs. . The matrix element ϕ H μν depends on contributions from all matrix elements of χ H .…”

Section: The Modified Neglect Of Diatomic Overlap Modelmentioning

confidence: 99%

“…Taking

^{ϕ} H_{μ ν}^{MNDO}

to be proportional to χ S μν has a long history and the initial idea is ascribed to Mulliken . In general, Equation was, however, found to be a poor approximation to the analytical value of ϕ H μν , irrespective of the chosen values for

β_{normall ((), μ)}^{Z_{normalI}}

This can be attributed to the fact that ϕ H μν is not necessarily proportional to χ S μν (for an example, see Figure ). Hence, not even the nodal structure of

^{ϕ} H_{μ ν} =^{ϕ} H_{μ ν} ({\overset{false˜}{R}}_{IJ})

is captured correctly.…”

Section: The Modified Neglect Of Diatomic Overlap Modelmentioning

confidence: 99%

“…Unfortunately, Coffey's analysis was restricted to the C 2 molecule and included several additional approximations (such as an averaging of one-and two-electron integrals). 158 It is not evident whether (and appears improbable 155,159 that) Coffey's analysis can easily be generalized to arbitrary polyatomic molecules. The success of the MNDO model indicates, however, that -at least in the context of all other invoked approximations -the Goeppert-Mayer-Sklar approximation is a satisfactory one.…”

Section: One-center One-electron Matrix Elementsmentioning

confidence: 99%

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Semiempirical molecular orbital models based on the neglect of diatomic differential overlap approximation

Husch

Vaucher

Reiher

2018

Int J of Quantum Chemistry

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Semiempirical molecular orbital (SEMO) models based on the neglect of diatomic differential overlap (NDDO) approximation efficiently solve the self-consistent field equations by rather drastic approximations. The computational efficiency comes at the cost of an error in the electron-electron repulsion integrals. The error may be compensated by the introduction of parametric expressions to evaluate the electron-electron repulsion integrals, the one-electron integrals, and the core-core repulsion. We review the resulting formalisms of popular NDDO-SEMO models (such as the MNDO(/d), AM1, PMx, and OMx models) in a concise and self-contained manner. We discuss the approaches to implicitly and explicitly describe electron correlation effects within NDDO-SEMO models and we dissect strengths and weaknesses of the different approaches in a detailed analysis. For this purpose, we consider the results of recent benchmark studies. Furthermore, we apply bootstrapping to perform a sensitivity analysis for a selection of parameters in the MNDO model. We also identify systematic limitations of NDDO-SEMO models by drawing on an analogy to Kohn-Sham density functional theory. K E Y W O R D SNDDO approximation, semi-empirical methods | INTRODUCTIONThe driving force for the development of semiempirical molecular orbital (SEMO) models has always been the desire to accelerate quantum chemical calculations. At the outset of the development of SEMO models in the middle of the last century, [1][2][3][4][5][6][7][8][9][10] the goal was to carry out electronic structure calculations for small molecules, which was not routinely possible with ab initio electronic structure methods at that time. Since then, theoretical chemistry has seen a remarkable development not only in terms of computational resources but also in terms of ab initio methodology. [11] One must not forget that most electronic structure methods which we apply routinely today, such as Kohn-Sham density functional theory (KS-DFT) [12] and coupled cluster theory, [13] were developed concurrently with today's SEMO models. As a consequence of algorithmic and methodological developments, [11] accurate ab initio electronic structure methods have long replaced SEMO models in their original areas of application (electronic structure calculations for small molecules). Nevertheless, SEMO models did not become extinct. Instead, they opened up different areas of application which can broadly be divided into three categories (see also Ref. [14] for a recent review): (1) simulations of very large systems such as proteins [15][16][17][18][19][20][21][22] and those with thousands of small molecules, [23,24] (2) calculations for a large number of isolated and unrelated medium-sized molecules, for example, in virtual high-throughput screening schemes for materials discovery [25,26] and docking-and-scoring of potential drug candidates, [27][28][29][30][31][32] and (3) entirely new applications such as real-time quantum chemistry where ultra-fast SEMO models allow the perception of visual and h...

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Improvement of the hydrogen bonding correction to MNDO for calculations of biochemical interest

Goldblum

1987

J Comput Chem

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Recent suggestions for correcting H -Acceptor interactions within MNDO, together with results of crystallographic analysis, were used to modify this SCF semiempirical calculation for multiple hydrogen bonded associations. Thermodynamic profiles for model systems of biochemical interest such as H20--H20, hydration of neutral and charged molecules, dimerizations and proton transfers show the advantages of this method. Its treatment of charges, bonding, geometries, energetics and vibrational frequencies is shown to be comparable to ab initio calculations with various basis sets. However, basic MNDO deficiencies and criteria applied for H-bonding result in some too high barriers for proton transfers.

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Analysis of the inadequacies of some semi‐empirical MO methods as theories of structure and reactivity

Cited by 20 publications

References 40 publications

Correlation contributions to the radical cation states of linear even polyenes: An open‐shell RHF‐CNDO/S(CI) analysis of the optical and photoelectron spectra

Correlation contributions to the radical cation states of linear even polyenes: An open‐shell RHF‐CNDO/S(CI) analysis of the optical and photoelectron spectra

Semiempirical molecular orbital models based on the neglect of diatomic differential overlap approximation

Improvement of the hydrogen bonding correction to MNDO for calculations of biochemical interest

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