Calculos de energias de ligação de camada interna pelo uso da teoria do funcional de densidade e suas aplicações / Density functional theory calculations of core-electron binding energies and applications

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

We calculated core-electron binding energies (CEBE) for 55 benzene and 161 phenol derivatives. Lindberg demonstrated that experimentally observed CEBE shifts (DCEBE) are linearly correlated to the Hammett substituent constants s. We investigated Lindberg s equation through the relationships between CEBEs calculated by the method of total energy difference DEKS (PW86x-PW91c)/TZP+Crel and the s constants for substituted benzene and phenol. We also separated the inductive (I) and resonance (R) effects as proposed by Taft. The goodness of fit for the constants in para and meta is better than that for the constants in ortho, where ortho, meta, and para indicate the position of the substituent S with respect to the carbon atom for which CEBE was calculated. The values of s experimentally determined in water yield better correlations than those determined in an ethanol-water mixture. We observed that the meta position and the I effect are weakly affected by the OH substituent (phenols) and the solvent (benzenes), as opposed to the R effect, which is strongly infiuenced by these factors. The para position shows an intermediate behavior, probably because it is composed of equal portions of R and I according to Taft s model. We estimated 69 values of sp and sm not described in the literature. Our results demonstrate that DCEBE can provide s values in a practical manner. In addition to performing CEBE calculations on carbon, we searched the best DEKS model for calculations involving 2p orbitals from Si, P, S, CI, and Ar in the gas phase. To that end we tested 51 functionals (Exc) , many of them combined with the potential (Vxc) known as SAOP, using 145 molecules containing the elements listed above. Each Exc was evaluated based on the absolute average deviation (AAD) between the calculated and observed values for each elemento The best methodology obtained for the series from Si to Ar was DEKS (scalar-ZORA+OPTX-LYP)/TZP / /HF /6-31G(d), yielding a weighted average of 0.26 eV for the 145 molecules tested; however, better results were obtained for individual elements. Exc = Becke88x-Perdew86 or mPW91x-PBEc yielded AAD = 0.10 eV for the Si compounds, and Exc = OPTX-Perdew exactly reproduced the average experimental value for Ar. The methodology DEKS (scalar-ZORA-SAOP+TPSS)/TZP//HF/6-31G(d) yielded AAD = 0.18 and 0.17 eV, respectively, for P and CI compounds. Using the best Exc obtained for CEBE 2p we estimated the work function of silicon compounds, calculated DCEBE for silicon oxide used as gate dielectric in MOSFET devices, and estimated excitation energies from the 2p orbital. All results are in good agreement with experimentally observed values.

ASSUNTO(S)

xps xps dft hammett sigma hammett sigma cebe dft cebe

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