[CP2K-user] Lattice Constant Optimization

[Brian Day]

As practice with crystalline materials, I was trying to determine the 
lattice constant of FCC Cu in CP2K. My approach was to vary the lattice 
constant, perform an energy calculation, and ultimately plot the energy vs. 
lattice constant to determine the minimum. However, when I did this the 
energy simply decreased as the lattice constant increased, without any 
minimum. I tried this both with and without D3. 

Here is an overview of my results. The first value is the lattice constant 
in angstrom, and the second is the energy in Hartree. 

             Cu - PBE                  Cu - PBE - D3 
3.45      -382.08717                -382.08717 
3.50      -382.32915                -382.32915 
3.55      -382.54857                -382.54857 
3.60      -382.74734                -382.74734 
3.65      -382.92688                -382.92688 
3.70      -383.08999                -383.08999 
3.75      -383.23701                -383.23701 
3.80      -383.37008                -383.37008 

I have also attached a sample input file. If anybody could offer some 
insight as to why I am seeing this behavior that would be greatly 
appreciated. 

Best,
     Brian
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