Fratesti_structuraloptimizations

Fratesti_structuraloptimizations - guido.fratesi@unimi.it

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guido.fratesi@unimi.it Structural optimizations Guido Fratesi ( Università di Milano )     Urbana, August 2006
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guido.fratesi@unimi.it Acetylene molecule (C 2 H 2 ) We want to use pw.x to find the optimized geometry of acetylene. Let us suppose we have the following guess for the structure (coordinates in atomic units):     C      0.000000000    0.000000000    0.000000000     C      2.100000000    0.000000000    0.000000000     H     -1.600000000    0.400000000    0.000000000     H      3.600000000   -0.400000000    0.000000000 pw.x   adopts periodic boundary conditions. We can put the molecule in a large box, whose size is a convergency parameter. Here, we choose a cube of side length 12 a.u. for quickness. Then: 1) Prepare the input file for the SCF calculation     (see next slide for other details), use PWgui if you prefer 2) Visualize the structure with XcrySDen     xcrysden --pwi acetylene.scf.in 3) Run the SCF calculation and look at forces on atoms.     pw.x < acetylene.scf.in > acetylene.scf.out
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guido.fratesi@unimi.it C 2 H 2  SCF: the input                  calculation = 'scf' ,                 restart_mode = 'from_scratch' ,                       outdir = 'your directory for temporary files/' ,  /                        ibrav = 1,                    celldm(1) = 12.D0,                          nat = 4,                         ntyp = 2,                      ecutwfc = 25.0D0 ,                      ecutrho = 160.0D0 ,                        nosym = .true. ,                  occupations = 'smearing' ,                      degauss = 0.005D0 ,  /                     conv_thr = 1.D-7 ,
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Fratesti_structuraloptimizations - guido.fratesi@unimi.it

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