We need 2 files

TiO2.cell

#TiO2.cell
 %BLOCK lattice_cart
 4.594 0.000 0.000
 0.000 4.594 0.000
 0.000 0.000 2.959
 %ENDBLOCK lattice_cart

 %BLOCK positions_frac
 Ti  0.000  0.000  0.000
 Ti  0.500  0.500  0.500
 O   0.305  0.305  0.000
 O  -0.305 -0.305  0.000
 O   0.805  0.195  0.500
 O  -0.805 -0.195  0.500
 %ENDBLOCK positions_frac

 symmetry_generate

 kpoint_mp_grid 3 3 3

TiO2.param

#TiO2.param
TASK                    : GEOMETRYOPTIMISATION
CUT_OFF_ENERGY          : 700 eV
XC_FUNCTIONAL           : PBE
WRITE_CELL_STRUCTURE    : true

Note

There are 2 ways to use the pseudopotentials:

- Using an external pseudopotential with extention .usp

- Using an internal pseudopotential created by the code during the execution according to type mentioned  in the param file which we will do it in this tutorial.


Execution

For serial calculation

/TiO2-GeoOpt$ castep.serial TiO2

For parallel calculation 

/TiO2-GeoOpt$ mpirun -np 4 castep.mpi TiO2

 

We will get the following files

/TiO2-GeoOpt$ ls
O_C19_PBE_OTF.usp  Ti_C19_PBE_OTF.usp  TiO2.bands  TiO2.bib  TiO2.castep  TiO2.castep_bin
 TiO2.cell  TiO2.check  TiO2.cst_esp  TiO2.geom  TiO2-out.cell  TiO2.param

Results

If we check the file TiO2.castep we will find the results of lattice parameters and atomic positions

                       Lattice parameters(A)       Cell Angles
                    a =      4.638479          alpha =   90.000000
                    b =      4.638479          beta  =   90.000000
                    c =      2.971775          gamma =   90.000000

                Current cell volume =            63.939178 A**3
                            density =             2.498180 amu/A**3
                                    =             4.148326 g/cm^3

                           -------------------------------
                                     Cell Contents
                           -------------------------------

            xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
            x  Element         Atom        Fractional coordinates of atoms  x
            x                 Number           u          v          w      x
            x---------------------------------------------------------------x
            x  O                 1         0.304951   0.304951  -0.000000   x
            x  O                 2        -0.304951  -0.304951   0.000000   x
            x  O                 3         0.804951   0.195049   0.500000   x
            x  O                 4        -0.804951  -0.195049   0.500000   x
            x  Ti                1         0.000000   0.000000   0.000000   x
            x  Ti                2         0.500000   0.500000   0.500000   x
            xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Titanium dioxide Anatase Crystal ...