LAMMPS Assignment

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Overview

This assignment was largely unable to be completed. Progress was made towards the objective of calculating the interatomic potentials as well as the calibration of MEAM potential using response surface.

Interatomic Potentials

The process for generating the interatomic potentials began with several potential inputs. The cohesive energy, 3.39 ev/atom, was set first. The parameters α and re were then calculated from the two equations below. The other parameters where chosen randomly.

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Once calculated, these parameters were input into the library.meam file seen below.

#MEAM data
# elt       lat     z       ielement     atwt
# alpha     b0      b1      b2           b3       alat    esub    asub
# t0        t1              t2           t3               rozero  ibar

'Al' 'fcc' 12 13 26.981500 
5.017950 10.030000 5.030000 8.130000 10.930000 4.050000 3.430000 3.878000 
1.948000e+01 18.080000 91.980000 23.280000 1 0 

Once the MEAM files were written the MatPro.py program, provided at [1], was run to calculate cohesive energy, lattice constant, bulk modulus, equilibrium volume, elastic constants c11, c12, and c44, surface formation energies for (100), (110), and (111), and defect energies vacancy and self-interstitial formation for the fcc structure. Once run the bounds set for each MEAM potential parameter had to be evaluated. This was done using a matlab script provided at [2]. This resulted in several output files. The first was Al_coarse_pot_eval_data.mat, provided below, and several text files which are also shown below.

LAMMPSout.jpg

Apara.jpg

Alpara.jpg

B0para.jpg

B1para.jpg

B2para.jpg

B3para.jpg

Cmaxpara.jpg

Cminpara.jpg

T0para.jpg

T1para.jpg

T2para.jpg

T3para.jpg

Calibration of MEAM potential using response surface

The sensitive parameters determined previously would be used to solve for the MEAM potential. Since the sensitive parameters were unable to be determined the potential was never calculated. A test run was performed which varied all twelve parameters. To reduce the time requirements N had to be significantly reduced, affecting the accuracy for many of the parameters. The results of this run are shown below.

LAMMPS.jpg

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