Calculation of ionization potentials

As to semiempirical calculation of ionization potentials, Koopmans theorem CNDO/2 and INDO ionization potentials are not so good, being usually about 4 eV too high. However, MINDO/2 Koopmans theorem... 

Table 1 References to Semi-empirical Calculations of Ionization Potentials, Electron Affinities and...

Gua has the lowest reduction potential among the four nucleobases (Table 10.2), and hence it is preferentially oxidized to its radical cation (for the calculation of ionization potentials of the DNA bases see Close 2004 Crespo-Hernandez et al. 2004), and this property makes Gua and its derivatives to stick out of the other nucleobases with respect to its different free-radical chemistry. In contrast, Thy and Cyt are good electron acceptors, while the purines are only poor ones in comparison (for the calculation of electron affinities, see Richardson et al. 2004). This is of special importance in the effects caused by the absorption of ionizing radiation by DNA. 

DiLabio, G. A. Pratt, D. A. Wright, J. S. Theoretical calculation of ionization potentials for disubstituted benzenes additivity vs non-additivity of substituent effects./. Org. Chem. 2000, 65, 2195-2203. 

The benchmark calculations of ionization potentials and electron affinities of the atoms and molecules in the G2 data set" calculated using the hybrid functional (B97) show that this functional is adequate. The average absolute deviation from experimental data amounts to 0.055 eV and 0.056 eV for ionization potential and electron affinity, respectively.51... 

Joanteguy S, Pfister-Guillouzo, Chermette H (1999) Asessment of density functional methods for the calculation of ionization potentials of unsaturated molecules, J Phys Chem A, 103, 3505-3511... 

Following the advances of the many-body theory started in physics in fifties and sixties of the twentieth century [1-8], many researchers in theoretical chemistry employed the ideas developed in physics and extended them to systems with a finite number of electrons [9-21]. Different software packages were developed soon [22] and applied to calculations of ionization potentials and electron affinities of various chemical systems [23-29]. The calculations appeared to be efficient, and the results were amazingly accurate. 

Some of the first applications of molecular-orbital theory in mass spectrometry were in calculations of ionization potentials of n-alkanes (see Streitwieser, 1961, for leading references). Strictly, these ionization potentials are a property of both the molecule and the ion produced, but often the effect of electron correlation in the ion is ignored (Koopmans, 1933) and resort is then made to adjustment of parameters to give good agreement between theory and practice. In the absence of experimental confirmation, such calculations must be viewed cautiously. 

Many ionization potentials have now been calculated for simple and complex molecules using more sophisticated self-consistent field treatments and, when the effect of electron correlation is considered, extremely good results may be obtained (e.g. Hush and Pople, 1954). Because ionization is rapid, the Franck-Condon principle applies in the calculation of ionization potentials, and the structure of the ion immediately after formation is essentially that of the molecule. On vibration, the geometry of the ion may change. 

Apart from calculations of ionization potentials, molecular-orbital arguments used up to now in mass spectrometry are heavily dependent on assumptions regarding ion structures or fragmentation processes. The molecular-orbital considerations may eventually be experimentally verified, but at present, the results must be regarded as interesting rather than informative. 

Calculations of ionization potentials represent a valuable tool for the interpretation of electron spectra. Unlike in semiempirical... 

Calculation of Ionization Potentials. It is possible to perform an approximate calculation of the ionization potentials of young soot particles and aromatic hydrocarbon molecules (31, 32, 33). Assuming the species to be an electrically conducting sphere or circular disk of radius r and capacitance C, the flrst ionization potential, i.e., the work required to remove one electron, is ... 

Multireference coupled cluster methods, which started development more recently, are generally divided into two types. Hilbert space CC methods use multiple reference functions to obtain a description of a few states, including the reference state (for a review see (4)). Fock space methods (for a review see (5)), on the other hand, provide direct state-to-state energy differences, relative to some common reference state. The Fock space approach is particularly well-suited to the calculation of ionization potentials (IPs), electron affinities (EAs), and excitation energies (EEs). For principal IPs and EAs, FSCC is equivalent (6, 7) to the EOM-IP and EOM-EA CC methods (1, 2, 7, 8). In this paper, we will focus primarily on the IP problem. 

Although it can be used in many other ways, the natural result of a (0,1) sector FSCC calculation is the energy of the vertical ionization process— extracting an electron from a molecule without allowing the geometry to relax to that of the resulting ion. Calculation of ionization potentials is, thus far, the predominant application of the FSCCSD method and such calculations will provide the bulk of the data for characterization of the approximate triples... 

A Fock space multireference coupled cluster method was described by Rittby and Bartlett <91TCA469>, applied to the calculation of ionization potentials and excitation energies of 1,2,4,5-tetrazines, and compared with conventional ab initio calculations and experimental results. 

Improvement in the calculation of ionization potentials is indicated by Table VI where we compare results for CO2, COS, and CS2 with... 

Table 7 References to various semiempirical and ab initio calculations of ionization potential for thiophene...

We now turn to the calculation of ionization potentials (IP s) within the SDCI formalism. The results for H2O using the 39-STO basis are shown in Table 4.8. The SDCI entry was obtained by performing separate SDCI calculations on H2O and H20 and subtracting the resulting energies. The... 

This form is convenient for the calculation of ionization potentials of closed-shell N-particle systems. 

Calculation of ionization potentials provides a good test of theoretical models. In general, there is a decrease by roughly a factor of two from the ionization potential of the atoms to the work function of the bulk metal. The decrease is not monatomic, but depends very much on particle geometry. There is also an odd-even alternation with the odd-atom clusters having a lower ion-ization potential, presumably because they are odd-electron systems as compared to closed-shell structures for the even-electron systems. These results agree fairly well with the few experimental results available for comparison. 

The calculations of ionization potentials were carried out using Kohn-Sham DFT, according to... 

A variety of modifications of the original methods is now available. AMI and PM3 have been extended for the treatment of transition-metal compounds by inclusion of d orbitals in the valence basis the Green s function technique has been implemented in MNDO-type methods for the calculation of ionization potentials and electron affinities a parameterized variational technique is used for the calculation of molecular polarizabilities and hyperpolarizabilities within the MNDO, AMI and PM3 methods [235]. 

T. Fox and P. Kollman, /. Phys. Chem., 100, 2950 (1996). Calculation of Ionization Potentials and C—H Bond Dissociation Energies of Toluene Derivatives. 

Carlson, T. A., Nestor, C. W. Jr, Wasserman, N., and McDowell, J. D. (1970) Comprehensive Calculations of Ionization Potentials and Binding Energies for Multiply-Charged Ions, USAEC Report ORNL-4562, Oak Ridge National Laboratory. 

Application of OVGF Method for Calculations of Ionization Potentials of Molecules... 

Table 9 Average Error in Calculations of Ionization Potentials for Different Semiempirical Methods...

It is instructive to make an immediate application (Smith and Day, 1975) to the calculation of ionization potentials. Thus, on putting ... 

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