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This page gives hints on how to to tune the computation of forces and stresses with the ABINIT package.

Introduction

Hellman-Feynman forces are computed from an analytical formula, and corresponds exactly to the limit of finite differences of energy for infinitesimally small atomic displacements when the ground-state calculation is at convergence. This feature is available for all the cases where the total energy can be computed. A correction for non-converged cases allows to get accurate forces with less converged wavefunctions than without it. The decomposition of the forces in their different components can be provided.

Stress can also be computed. This feature is available for all the cases where the total energy can be computed (except wavelets). The decomposition of the stresses in their different components can be provided. A smearing scheme applied to the kinetic energy [[ecutsm]] allows one to get smooth energy curves as a function of lattice parameters and angles. A target stress can be given by the user ([[strtarget]]), the geometry optimization algorithm will try to find the primitive cell and atomic positions that deliver that target stress.

The computation of forces and stresses is optional, see [[optforces]] and [[optstress]]. They are used to define SCF stopping criteria ([[toldff]], [[tolrff]]) or geometry optimization stopping criteria ([[tolmxf]]). For the geometry optimization, combined cell shape and atomic position optimization need a conversion scale, set by [[strprecon]].

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Selected Input Files

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Tutorials