Dear Amirhossein Bayani,

The following data may be helpful:

Electron work functions of several metals (Au, W, Ag, Cu, Mo, Ti, Al) and Si at atmospheric conditions have been measured by the method of the static capacitor with an ionized gap between the electrodes. Results for all samples, excluding Au, Al and Si, conform to reference data with an accuracy of +/- 1.0%. For samples Au, Al and Si, the electron work function values conform to reference data after short-time heat treatment at atmospheric conditions at 200 degrees C (for Al) and 600 degrees C (for Au, Si).

https://www.researchgate.net/publication/10570956_Measurements_of_contact_potential_difference_work_functions_of_metals_and_semiconductors_surface_by_the_static_ionized_capacitor_method

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Despite of its huge successes in total energy related applications, the Kohn-Sham scheme of density functional theory (DFT-Kohn-Sham) cannot get reliable single particle excitation energies for solids. In particular, it has not been able to calculate the ionization potential (IP), one of the most important material parameters, for semiconductors. We illustrate that an approximate exchange-only optimized effective potential (EXX-OEP), the Becke-Johnson exchange, can be used to largely solve this long-standing problem. For a group of 17 semiconductors, we have obtained the IP’s to similar accuracy as the much more sophisticated GW approximation (GWA), with the computational cost of only LDA/GGA. The EXX-OEP, therefore, is likely as useful for solids as for finite systems. For solid surfaces, the asymptotic behavior of the vxc has similar effects as for finite systems which, when neglected, typically causes the semiconductor IP’s to be underestimated by about 0.2 eV. This may partially explain why standard GWA systematically underestimates the IP’s, and why using the same GWA procedures has not been able to get accurate IP and band gap at the same time.

https://arxiv.org/pdf/1603.01428.pdf

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