Copy all files from the tutor/diamant directory to a work directory, and proceed step by step:
cubic diamond comment line 3.7 universal scaling factor 0.5 0.5 0.0 first Bravais lattice vector 0.0 0.5 0.5 second Bravais lattice vector 0.5 0.0 0.5 third Bravais lattice vector 2 number of atoms per species direct direct or cart (only first letter is significant) 0.0 0.0 0.0 positions 0.25 0.25 0.25The positions can be given in direct (fractional) or cartesian coordinates. In the second case positions will be scaled by universal scaling factor.
4x4x4 Comment 0 Automatic generation of k-points Monkhorst M use Monkhorst Pack 4 4 4 grid 0 0 0 shiftThe first line is a comment, if the second line is zero k-points are generated automatically using a Monkhorst-Pack grid (first character in third line equal ``M''). With the supplied KPOINTS file a Monkhorst-Pack grid without shift (fifth line) will be used for the calculation.
> makeparamand copy the lines written to the screen to the param.inc file. The param.inc is ``included'' during the compilation of the param.F and fft3d...F file of VASP.3.X and contains information about the maximum size of the system. It this particular case it will be similar to
C C automatic param.inc file C C-----General parameters always needed ... PARAMETER(NGX = 12,NGY = 12,NGZ = 12, & NGXF= 20,NGYF= 20,NGZF= 20) PARAMETER(NTYPD=1,NIOND= 2,NBANDS= 7,NKDIM= 10) PARAMETER(NRPLWV= 203,NPLINI= 7) PARAMETER(NRPLWL= 1,NBLK= 32,MCPU= 1) C-----Parameter for non-local contribution PARAMETER(LDIM=4,LMDIM= 8,LDIM2=(LDIM*(LDIM+1))/2,LMYDIM=10) PARAMETER(IRECIP=1,IRMAX= 1,IRDMAX= 2561) C-----extra parameters: PARAMETER(IALLD=0,IRMMD=4,NEMPTY=4,ISPIND=1,IGRAD=1)most parameters in the param.inc file are only necessary to allocate sufficient work space, but some do influence the calculation. These parameters are NGX Y Z NG(X,Y,Z)F and to a smaller extend NBANDS. NGX,Y,Z and NG(X,Y,Z)F control the size of the FFT meshes (second mesh is for the representation of the augmentation charges) used in the calculation. They must be sufficiently large to avoid the so called wrap around errors (see section 10.4). makeparam usually allows by default a small wrap around (3/4 of the required value are used for the FFT-meshes), together with the default energy cutoff the errors are usually negligible (less than 1 meV per atom).
> getvaspThe required parts (two subroutines) of vasp will be recompiled and a working copy of the vasp program will be copied to your local directory.
> vaspYou will get an output similar to
POSCAR found : 1 types and 2 ions Automatic xc-table for CA file io ok, starting setup WARNING: wrap around errors must be expected entering main loop N E dE d eps ncg rms rms(c) CG : 1 -0.27655216E+03 -0.2765E+03 -0.1962E+03 146 0.558E+02 CG : 2 -0.30480031E+03 -0.2824E+02 -0.9664E+01 163 0.998E+01 CG : 3 -0.31085987E+03 -0.6059E+01 -0.3783E+00 166 0.160E+01 0.790E-01 CG : 4 -0.31052425E+03 0.3356E+00 -0.1041E+00 156 0.103E+01 0.123E-01 CG : 5 -0.31052313E+03 0.1126E-02 -0.6119E-03 177 0.713E-01 0.185E-02 CG : 6 -0.31052312E+03 0.4535E-05 -0.8772E-05 119 0.109E-01 1 F= -.20028156E+02 E0= -.20028156E+02 d E =0.000000E+00 writing wavefunctionsVasp is using a selfconsistency cycle with a Pulay mixer and an iterative matrix diagonalization scheme to calculate the KS-groundstate. Each electronic step consists of one step in the iterative matrix diagonalization and one mixing step. Progress is written to stout (and to the file OSZICAR).
N counts the electronic iterations, E the current free energy, dE the change in the free energy from the last to the current step and d eps the change in the band-structure energy. ncg the number of evaluations of the Hamiltonian acting onto a wavefunction, rms the norm of the residuum ( ) of the trial wavefunctions (i.e. their approximate error) and rms(c) the difference between input and output charge density. In the first few steps the density and the local potentials are not updated to converge the wavefunctions to a reasonable accuracy (rms(c) is therefore not shown). Then the update of the charge density starts, in this case only three updates are required to obtain a sufficiently accurate groundstate.
The final line gives energy information after obtaining convergence. The most important value is the total free energy F (at this point the energy of the reference atom has been subtracted).
Much more information (like forces and stress tensor) can be found in the OUTCAR file. Please read this file to get an impression what information can be found.
Another important file is the WAVECAR file which contains the final wavefunction. VASP usually tries to read this file on startup to speed up the calculations. At the end of the calculations the file is written (or if it exists overwritten).
There will be an error, correct the param.inc file and type getvasp again. The error is due to the fact that one array was not sufficiently large. (The arrays were set up for a specific volume, changing the volume will change the requirements for some work arrays, it is always safest to run the makeparam utility with the largest volume in mind, and to double then the value IRDMAX in the param.inc file).
NSW = 10 ! allow 10 steps ISIF = 2 ! relax ions only IBRION = 2 ! use CG algorithmto the INCAR file.
Once again you will get an error; you have to increase the number of k-points in the param.inc file (NKDIM) as the symmetry of the system has been broken. Do that and proceed with the calculation. (At this point you might find it helpful to read section 7.19).
To find the minimum a line minimizations of the energy into the direction of the forces is done (see 7.19), for the line minimization a "small" trial step into the direction of the force is done and the energy change is evaluated, this allows to calculate the position of the minimum. For Carbon, the trial step is much to large you can reduce it by setting POTIM in the INCAR file:
POTIM = 0.1 ! reduce trial step to 10 %Do that and start once again from a more exited structure (0.20,0.20,0.20).
After a relaxation job (or a molecular dynamics run) the final positions are written to the file CONTCAR. This file has the same format as the POSCAR file. If one wants to continue calculations with the relaxed positions simply copy CONTCAR to POSCAR.
ISIF = 3 ! relax ions + volumeand start once again. Positions and cell shape will be relaxed.
Do not forget to check the OUTCAR file.
EDIFF = 1E-7 ! very high accuracy required 10^-7 eVin the INCAR file. Start from the CONTCAR file of the last calculation (i.e. copy CONTCAR to POSCAR). You will get some warnings, they point out that your FFT mesh is not sufficient for this calculation. This is true in principle, but in practice the results will be only marginally affected by increasing NGX, NGY, NGZ.
Then use the default cutoff. The stress is now -43 kB. This gives you an estimation of the possible errors. (You might correct the relaxation by setting
PSTRESS = -43 ! Pulay stress = -43 kBin the INCAR file. But we do not recommend this procedure, it is definitely preferable to increase ENCUT.)