PACS. 31.15.Ar -Ab initio calculations. PACS. 73.30.+y -Surface double layers, Schottky barriers, and work functions. PACS. 68.35.Gy -Mechanical properties; surface strains. PACS. 82.45.Fk -Electrodes.Abstract. -We explore an efficient way to numerically evaluate the response of the surface stress of a metal to changes in its superficial charge density by analysis of the strain-dependence of the work function of the uncharged surface. As an application we consider Au(111), (110) and (100) surfaces, employing density functional calculations. The sign of the calculated response parameter can be rationalized with the dependence of the surface dipole and the Fermi energy on strain. The numerical value falls within the range indicated by experiment. The magnitude can explain the experimentally observed volume changes of nanoporous materials upon charging.Recent experiments reveal a macroscopic expansion or contraction when high surface area metals with nanometer-sized porosity are electrically charged, the signature of changes in the surface bond forces when a space-charge layer is generated [1,2]. The parameter which quantifies these forces in the continuum description of solid surfaces, the surface stress, f , is a topic of current interest in surface science, since it is intricately related to the surface electronic structure and bonding, and since it is relevant for reconstruction as well as for the stress in thin film devices [3,4]. Furthermore, the impact of the energy-conjugate quantity to f , the tangential strain e, on the surface electronic structure is being recognized as central for the catalytic activity of metal surfaces [5,6]. The response of f to changes in the superficial excess charge density (per area), q, relates to fundamental issues in electrochemistry, such as electron transfer in surface-adsorbate bonds or microscopic processes in the electrochemical double layer [3,[7][8][9]. Experiments finding a stronger response when there is less adsorption point towards the effect of q on the bonding in the metal surface as a decisive factor [10,11]. Yet, the microscopic processes linking q to forces and relaxation at metal surfaces are c EDP Sciences

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First-principles studies on the intrinsic mechanical properties of various materials and systems through ab initio tensile and shear testing simulations based on density-functional theory are reviewed. For various materials, ideal tensile and shear strength and features of the deformation of bulk crystals without any defects have been examined, and the relation with the bonding nature has been analyzed. The surfaces or low-dimensional nano-structures reveal peculiar strength and deformation behavior due to local different bonding nature. For grain boundaries and metal/ceramic interfaces, tensile and shear behaviors depend on the interface bonding, which impacts on the research of real engineering materials. Remaining problems and future directions in this research field are discussed.

The PbTiO 3 ͑001͒ surface structure with ferroelectric ͑FE͒ polarization parallel to the surface and its response to tangential strain have been studied using ab initio density functional theory calculations with the local density approximation. We find ͓110͔-oriented ferroelectricity is more stable than ͓100͔-oriented under zero and nonzero strain in both TiO 2 and PbO terminations. Tensile strain enhances the FE distortion and suppresses the antiferrodistortive rotation, while the opposite trend is found under compression. The FE polarization direction alters with respect to the variation of the uniaxial strain owing to the preference of the polarization along the longer axis of rectangular lattices. The sensitivity of the FE rotation significantly differs depending on the layer at PbO-terminated c͑2 ϫ 2͒ surface, leading to the variation of polarization directions among the layers under uniaxial strain.