====== Surface energies of Copper high-symmetry surfaces ======
In this exercise we will compute the surface energies of Cu using the EAM potential.
As a reference, we report the table from the Gross book:

{{screen_shot_2014-03-07_at_6.55.49_am.png?direct&500 |http://example.com|External Link}}


  - Copy the files from  from the wiki: {{exercise_3.1.zip|exercise_3.1.zip}} (**all inputs are commented**) into a new directory
  - Use the batch **run_cp2k_lattice** to run a chain of simulations on a Cu bulk system. From the output **lat.out** check the lattice constant corresponding to minimum cohesive energy **PER ATOM** (divide by the number of particles, find it out!), you will need it later
  - Run the optimizations 100.inp, 110.inp, 111.inp ---- look at the corresponding initial coordinate files 100.xyz, 110.xyz, 111.xyz. 
  - In vmd, you can also open a console, and give the command **pbc set { a b c 90 90 90 }**  where a, b, c can be extracted from the cp2k input file. Then you can make several periodic copies for visualization.
  - Compute the three surface energies: you need to compute the area, subtract bulk contribution, take care of the units.
  - In the class we will learn how to compute the Wulff crystal from these three numbers.
  - Basically, you should edit the input file "DP", replacing the column beginning with **"PUT_HERE_THE_XXX_SURFACE_ENERGY"** with quantities that are proportional to the three surface free energies (see Wulff theorem). Note that for the {100} and {110} surfaces you need to edit **TWO** lines each, since the **z** direction is treated differently in this program. 
  - At this point, you run the program with the command **./sowos.v02.00.02.x** 
  - There will be many output files. Important are 
  -   * the atomistic model **out.atomistic-inside-gnuplot.xyz** which will contain many atoms if you chose a proportionality constant in the file DP which is too large. If you appropriately modify it (how?) you can have a xyz file to be opened in vmd.  
  -   * the **out.plot-gnuplot.plt** file. If you launch gnuplot, then "**load "out.plot-gnuplot.plt"**  a plot of the crystal will be shown. To have it more or less to scale in all directions: **set xrange [-80:80];set yrange [-80:80]; set view equal xyz; replot**
  -   * you can rotate with the mouse!

<note important>**Assignment: use the cluster generated with SOWOS as an input configuration for a cluster optimization with cp2k. Comment on the final geometry. BEWARE OF THE CELL! It is not a periodic system!**</note>


<note tip>documentation on **SOWOS** can be found at [[http://www.danielescopece84.altervista.org/sowos.html|the web site of Daniele Scopece]]</note>