Is HAM/3 (hydrogenic atoms in molecules, version 3) a semiempirical version of dft (density functional theory) for ionization processes?

Abstract

Nós calculamos os potenciais de ionização verticais (VIPs) de nove moléculas pequenas, bem como, os potenciais de uracil e do C 2 F 2 usando diferentes métodos: i) semi-empírico HAM/3; ii) semi-empírico AM1; iii) não empírico Teoria do Funcional de Densidade (TFD) com os modelos uDI(B88-P86)/cc-pVTZ e -ε(SAOP)/TZP; iv) ab initio HF/cc-pVTZ. Os resultados numéricos obtidos com HAM/3 são mais próximos dos resultados obtidos com o TFD do que o Hartree-Fock (HF). Nós também calculamos as energias de ligação de elétrons do caroço (CEBE) da anilina, nitrobenzeno, e p-nitroanilina com o HAM/3 e a TFD empregando o método ∆E. O modelo de DFT designado como ∆E KS (PW86-PW91)/TZP produziu resultados precisos de CEBE, com desvio médio absolutos de 0,14 eV. Enquanto que a magnitude absoluta dos CEBEs calculados pelo método HAM/3 tem um erro de menos de 3 eV, os deslocamentos químicos (∆CEBE) têm erros menores que 0,55 eV. Mesmo que os resultados de CEBE não apresentem uma resposta definitiva à pergunta do título, as tendências nos VIPs indicam que o HAM/3 não se aproxima do TFD com potenciais de troca-correlação precisos, mas indicam uma proximidade com funcionais semelhantes ao B88-P86.We calculated valence-electron vertical ionization potentials (VIPs) of nine small molecules, plus uracil and C 2 F 4 , by several different methods: semiempirical HAM/3 and AM1 methods, different nonempirical DFT models such as uDI(B88-P86)/cc-pVTZ and -ε(SAOP)/TZP, and ab initio Hartree-Fock (HF) /cc-pVTZ. HAM/3 reproduced numerical values more closely to those calculated by the nonempirical DFTs than to those obtained by HF method. Core-electron binding energies (CEBEs) of aniline, nitrobenzene and p-nitro aniline, were also calculated by HAM/3 and nonempirical ∆FT using DE method. A nonempirical DFT model, designated as ∆E KS (PW86-PW91)/TZP model, resulted accurate CEBEs (average absolute deviation of 0.14 eV) with high efficiency. Although absolute magnitude of HAM/3 CEBEs has error as much as 3 eV, the error in the chemical shifts ∆CEBE is much smaller at 0.55 eV. While the CEBE results do not lead to any definite answer to the question in the title, the trends in valence-electron VIPs indicate that HAM/3 does not approximate DFT with accurate exchange-correlation potentials, but seems to simulate approximate functionals such as B88-P86.Keywords: HAM/3, DFT, vertical ionization potential, CEBE, ESCA IntroductionThe semiempirical molecular orbital (MO) method known as Hydrogenic Atoms in Molecules, Version 3 (HAM/3) was developed by group of Lindholm and coworkers in 1977. 1 The method has been successfully applied to the calculation of mainly vertical ionization potentials (VIPs), excitation energies, and electron affinities of wide variety of molecules. Some selected works are listed in references 2-7. However, extensions of HAM/3 to the calculation of X-ray emission spectra, 8 Auger electron spectra, 9 valence-electron shake-up satellites, 10 core-electron shake-up satellites, 11 and relative intensities for valence region of X-ray p...

An experimental and theoretical study into the valence electronic structure of bicyclo[2.2.1]hepta-2,5-dione

“…The accuracy of DFT calculated orbital energies has traditionally been found to be in poor agreement with experimental PES and EMS binding energy measurements, as Koopmans' theorem [25] does not hold for Kohn-Sham orbital energies. However, recent developments in DFT using the 'meta-Koopmans' theorem [26][27][28][29], an analogue of Koopmans' theorem for DFT, can generate vertical ionization potential (VIP) energies of molecular species with an accuracy up to 0.2 eV, using the recently developed orbital-dependent statistical average of different model orbital potentials (SAOP) [27,30,31] method, which is particularly successful in modelling the XC functional [28]. The SAOP potential provides quite good VIPs, including those from the inner valence region, provided that there are no appreciable shake-up satellites [29].…”

“…However, recent developments in DFT using the 'meta-Koopmans' theorem [26][27][28][29], an analogue of Koopmans' theorem for DFT, can generate vertical ionization potential (VIP) energies of molecular species with an accuracy up to 0.2 eV, using the recently developed orbital-dependent statistical average of different model orbital potentials (SAOP) [27,30,31] method, which is particularly successful in modelling the XC functional [28]. The SAOP potential provides quite good VIPs, including those from the inner valence region, provided that there are no appreciable shake-up satellites [29]. This is generally the case for orbitals with binding energies below 20 eV, i.e.…”

Calculation of ionization potential and chemical hardness: A comparative study of different methods

“…The asymptotically corrected model exchange correlation potential, i.e., statistical average of orbital potential (SAOP), 44 has also been used to calculate the ionization potential and chemical hardness values. It has been shown earlier that the negative of HOMO energy (− E HOMO ) obtained through SAOP is equal to the vertical ionization potential for different types of molecules 44–46. The DFT calculations have been performed with an atomic basis set of Slater‐type orbitals of triple‐Zeta quality including one set of polarization functions on each atom, denoted as TZP 47.…”

Chemometric modeling of core-electron binding energies

“…The presence of several similar or different functional groups and chemical elements besides carbon and hydrogen is a certain enterprise in terms of experimental or theoretical ESCA/CEBE studies. Modern semi-empirical and DFT methodologies for calculation of CEBEs for various chemical elements [23,[28][29][30] enable expansion of such studies to diverse molecules without having measured ESCA binding energies/shifts. Calculated CEBEs/CEBEs shifts have shown to be potential local molecular descriptors in (quantitative) structure-activity relationships (Q)SAR, quantitative structure-property relationships (QSPR), linear free energy relationships (LFER), and related studies [31][32][33].…”