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Assignment 2.

Vacancies and Free surfaces in Fe

Fe can exist in two different crystal structures, fcc and bcc . These two structures relate to widely used austenitic and ferritic steels, respectively. In this assignment you will be comparing the properties of various defects in both crystal structures.

In this assignment you will run the simulation codes yourself using the forms based site.
The first part of the assignment is to simulate the structure and energy of a vacancy in both crystal structures. The lattice parameter for the bcc Fe is 2.87 Angstroms and the cohesive energy should be 4.28 eV. The cohesive energy of the fcc face is 4.196 eV at a lattice parameter of 3.515 Angstroms.
Locate the vacancy at the center of the simulation block and use periodic boundary conditions in all three directions. A block of 4x4x4 unit cells will be adequate.
In the second part you will calculate structure and energies of free surfaces in both crystal structures. Create the surface by opening up the block in two parts through a planar shear fault consisting of a displacement in the y direction of 10 Ansgrtoms( greater than the range of the potential). Your block should have the y axis perpendicular to the surface you will calculate. Choose (100), (110) or (111). specify periodic boundary conditions along the directions contained in the surface plane (x and z) and fixed along the directions perpendicular to the surface (y).

You should produce a report in the format of a Web page. If appropriate, we may incorporate all your pages developed in this assignment to the Web class module on this topic. You are encouraged to be creative in the analysis of the results

Your report should contain the following:

A n introductory description of the material being simulated and a brief research of its practical applications and relevance of the two particular defects being simulated.
A report of the obtained vacancy formation energies and the atomic displacements observed.
A report of the obtained surface energies and the atomic displacements observed.