Force field (physics)

Abstract: We address the problem of finding interatomic force fields for silicas from ab initio calculations on small clusters. It is shown that the force field cannot be determined from cluster data alone; incorporation of bulk-system information into the force field remains essential. Bearing this in mind, we derive a force field based on both microscopic (ab initio) and macroscopic (experimental) data. This force field combines accuracy with transferability to other polymorphs. The possibility of parametrizing other elements is also demonstrated.

Abstract: The parallel between the classical theory of elasticity and the modern physical theory of the solid state is incomplete; the former has nothing analogous to the concept of the force acting on an imperfection (dislocation, foreign atom, etc.) in a stressed crystal lattice. To remedy this a general theory of the forces on singularities in a Hookean elastic continuum is developed. The singularity is taken to be any state of internal stress satisfying the equilibrium equations but not the compatibility conditions. The force on a singularity can be given as an integral over a surface enclosing it. The integral contains the elastic field quantities which would surround the singularity in an infinite medium, multiplied by the difference between these quantities and those actually present. The expression for the force is thus of essentially the same form whether the force is due to applied surface tractions, other singularities or the presence of the free surface of the body (‘image force’). A region of inhomogeneity in the elastic constants modifies the stress field; if it is mobile one can define and calculate the force on it. The total force on the singularities and inhomogeneities inside a surface can be expressed in terms of the integral of a ‘ Maxwell tensor of elasticity’ taken over the surface. Possible extensions to the dynamical case are discussed,

Abstract: A guided tour through modern charge density analysis.- Electron densities and related properties from the ab-initio simulation of crystalline solids.- Modeling and analysing thermal motion in experimental charge density studies.- Spin and the Complementary Worlds of Electron Position and Momentum Densities.- Past, present and future of charge density and density matrix refinements.- Using wavefunctions to get more information out of diffraction experiments.- Local Models for Joint Position and Momentum Density Studies.- Magnetization densities in material science.- Beyond Standard Charge Density Topological Analyses.- On the Interplay Between Real and Reciprocal Space Properties.- Intermolecular interaction energies from experimental charge density studies.- Chemical Information from Charge Density Studies.- Charge density in materials and energy science.- A generic force field based on Quantum Chemical Topology.- Frontier Applications of Experimental Charge Density and Electrostatics to Bio-Macromolecules.- Charge densities and crystal engineering.- Electron Density Topology of Crystalline Solids at High Pressure.- Bonding changes along solid-solid phase transitions using the Electron Localization Function approach.- Multi-temperature electron density studies.- Transient Charge Density Maps from Femtosecond X-Ray Diffraction.- Charge density and chemical reactions: a unified view from Conceptual DFT.