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Publication# Multiscale quantum/atomistic coupling using constrained density functional theory

Abstract

Multiscale coupling of a quantum mechanical (QM) domain to a coarser-scale material description in a larger surrounding domain should yield forces and energies in the QM domain that are the same as would be achieved in a QM simulation of the entire system. Here, such a coupling is achieved by using constrained density functional theory (DFT) in which the quantum mechanical interaction between the domains is captured via a constraint potential arising from an imposed constraint on the charge density in a boundary region between the two domains. The implementation of the method, including the construction of the constraint charge density and the calculation of the constraint potential, is presented. The method is applied to problems in three different metals (Al, Fe, and Pd) and is validated against periodic DFT calculations. The method reproduces the QM charge density and magnetic moments of bulk materials, produces a reasonable edge dislocation core structure for Fe, and also gives accurate vacancy formation energy for Al and chemisorption energy on a flat Pd surface. Finally, the method is used to study the chemisorption energy of CO on a stepped Pd surface. In general, the method can mitigate fictitious interactions between surface steps and other extended defects, and accommodate long-range deformation fields, and thus improves upon periodic DFT calculations. DOI: 10.1103/PhysRevB.87.054113

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Related concepts (12)

Boundary layer

In physics and fluid mechanics, a boundary layer is the thin layer of fluid in the immediate vicinity of a bounding surface formed by the fluid flowing along the surface. The fluid's interaction with the wall induces a no-slip boundary condition (zero velocity at the wall). The flow velocity then monotonically increases above the surface until it returns to the bulk flow velocity. The thin layer consisting of fluid whose velocity has not yet returned to the bulk flow velocity is called the velocity boundary layer.

Density functional theory

Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases. Using this theory, the properties of a many-electron system can be determined by using functionals, i.e. functions of another function. In the case of DFT, these are functionals of the spatially dependent electron density.

Fictitious force

A fictitious force is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as a linearly accelerating or rotating reference frame. It is related to Newton's second law of motion, which treats forces for just one object. Passengers in a vehicle accelerating in the forward direction may perceive they are acted upon by a force moving them into the direction of the backrest of their seats for instance.