[show abstract][hide abstract] ABSTRACT: We demonstrate a correlation between the frequency of the nu(CO) stretch vibration of chemisorbed CO and the surface stress of Cu substrates. The surface stress is tailored by pseudomorphic growth of Cu multilayers on mismatched single crystal substrates. The CO stretch frequency is found to vary linearly with the inherent copper strain. An intuitive model to explain this intriguing relation is proposed.
[show abstract][hide abstract] ABSTRACT: Direct evidence for the effect of local strain at a surface on the bonding strength for adsorbates is presented. Scanning tunneling microscopy revealed that adsorbed oxygen atoms on Ru(0001) surfaces are located preferentially on top of nanometer-size protrusions above subsurface argon bubbles, where tensile strain prevails, and are depleted around their rim in regions of compression, relative to the flat surface. Such effects can be considered as the reverse of adsorbate-induced strain, and their direct local demonstration can be used to test theoretical predictions.
[show abstract][hide abstract] ABSTRACT: Generalized gradient approximations (GGA’s) seek to improve upon the accuracy of the local-spin-density (LSD) approximation in electronic-structure calculations. Perdew and Wang have developed a GGA based on real-space cutoff of the spurious long-range components of the second-order gradient expansion for the exchange-correlation hole. We have found that this density functional performs well in numerical tests for a variety of systems: (1) Total energies of 30 atoms are highly accurate. (2) Ionization energies and electron affinities are improved in a statistical sense, although significant interconfigurational and interterm errors remain. (3) Accurate atomization energies are found for seven hydrocarbon molecules, with a rms error per bond of 0.1 eV, compared with 0.7 eV for the LSD approximation and 2.4 eV for the Hartree-Fock approximation. (4) For atoms and molecules, there is a cancellation of error between density functionals for exchange and correlation, which is most striking whenever the Hartree-Fock result is furthest from experiment. (5) The surprising LSD underestimation of the lattice constants of Li and Na by 3–4 % is corrected, and the magnetic ground state of solid Fe is restored. (6) The work function, surface energy (neglecting the long-range contribution), and curvature energy of a metallic surface are all slightly reduced in comparison with LSD. Taking account of the positive long-range contribution, we find surface and curvature energies in good agreement with experimental or exact values. Finally, a way is found to visualize and understand the nonlocality of exchange and correlation, its origins, and its physical effects.
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