Hi
You have only performed a single point energy calculation (RUN_TYPE ENERGY). You cannot optimize the lattice constant with this kind of simulation. Please refer to the tutorials on how to perform such a calculation, e.g. here: https://www.cp2k.org/events:2019_cp2k_workshop_ghent:index under "Geometry and cell optimization of NaCl clusters"
Cheers,
Fabian
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Dear Sumit
A supercell of (2x2x2) has to contain 2*2*2=8 times the number of atoms of the unit cell. So It can never have an odd number as in your case 63. You should follow a tutorial on how to prepare such a structure, e.g. with ASE. Here, for example, you find instruction on how to build a crystal: http://exciting-code.org/lithium-atomic-simulation-environment. Once you have the ASE Atoms object building the supercell is as easy as atoms*(2,2,2). When you have a correct crystal, make sure that the &CELL section in the cp2k input matches the lattice dimensions of the crystal. You cannot just use an arbitrary number.
CELL_OPT will optimize both the atom positions as well as the lattice dimensions.
Fabian
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cp2k prints "CELL| Vector" after each iteration of the optimizer. From this you can calculate the lattice constant.
The lattice constant usually refers to the dimension of a unit cell, therefore it does not change when you create a supercell. The cell dimensions, however, differ between the unit and supercell.
Fabian
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