DFT for the Cohesive Properties of Metals

Simple models aside, if we choose to perform a self-consistent DFT calculation in which we explicitly treat the ionic lattice with, for example, a PP or full potential treatment, what level of accuracy can we expect to achieve As always, the answer depends on the properties we are interested in and the exchange-correlation functional we use. DFT has been used to compute a whole host of properties of metals, such as phonon dispersion curves, electronic band structures, solid-solid and solid-liquid phase transitions, defect formation energies, magnetism, superconducting transition temperatures, and so on. However, to enable a comparison between a wide range of exchange-correlation functionals, we restrict ourselves here to a discussion of only three key quantities, namely, (i) (ii) ao, the 

2) The PBE (GGA) functional results are generally closer to experiment than LDA. The average errors for these metals are H-1.3% for the lattice constants, and —5% for both the bulk moduli and cohesive energies. Naturally, this improvement leads to larger lattice constants, smaller bulk moduh, and smaller cohesive energies. Indeed, it is now clear that performance is very sensitive to the sohds considered [68]. 

3) The TPSS (meta-GGA) fimctional is somewhat difiicult to assess. For lattice constants, it is significantly better than LDA and GGA with an error of only 0.5%, getting aU four metals within 0.04 A. For the bulk moduh, however, it is not as accurate, with an error of 11%, and for , we are not aware of any reported values. There is now a revised TPSS functional, which for many properties improves over the original TPSS functional [35]. 

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Table 2.1 lists a number of DFT and experimental values for a simple metal Al, two noble metals Cu and Ag, and a transition metal with an unfilled d shell Pd. One example from each of the first four generations of exchange-correlation functional is given so as to provide a flavor of the current state of DFT for the cohesive properties of metals. In addition to the LDA, we show results from the PBE (GGA), TPSS (meta-GGA), and PBEO (hybrid) functionals. Let us consider each functional in turn and see what general conclusions can be drawn ... 

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