To successfully run VASP calculations, you must be familiar with the types of files VASP needs for computations. See Getting Started with VASP
Note: It is extremely important to maintain consistency between input files, even down to ensuring that the ordering of atoms in POTCAR and POSCAR are consistent. Without this, the computations will either not run correctly or not at all.
Making the POTCAR File
The final POTCAR file used for computations is the result of concatenation of 1 or more POTCAR files which can be obtained from the VASP database. Once the proper files are downloaded, the final POTCAR is made in the command-line prompt using terminal: cat (POTCAR of one atom) (POTCAR of the second atom) (etc.) >POTCAR.
Obtaining the atomic POTCAR files
If you're using NOVA, creating the POTCAR is easy as pie, just select the ones you want.
The psuedopotentials are stored within VASP, so to get the ones you need, load the VASP module and explore until you find them. Then you can concatenate the needed psuedopotentials together in a new file— your POTCAR.
Making the POSCAR File
To get started, read the POSCAR about file in the VASP online manual.
The POSCAR file includes the structural information for the system under investigation. It requires several important lines of code to function properly. They are explained in the above help file, but are also summarized below for convenience.
When writing the POSCAR file, it is important to note that the presence of a scaling factor (also known as the lattice constant), represented by writing line 2 as "X.XXXX !scaling parameter." This has the effect of rescaling lattice vectors and all coordinates accordingly.
Most CIFs from which our structural data is obtained give data on the unit cell parameters in the a,b,c (lengths) and alpha,beta,gamma (degrees) format. However, VASP uses lattice vectors in 3-space instead. To convert to this notation, open the CIF of the model compound using VESTA. Then, export the data using File>Export Data>P1 Structure. Open this P1 structure (filename.p1) using notepad, and the lattice vectors are listed at lines (2),(3), and (4).
Making the INCAR File
As mentioned in Getting Started with VASP, the INCAR file is what directs the computations the package performs on the system at hand. For our purposes, the INCAR file can be relatively simple, with many tags left as default for the majority of jobs we perform. Some of the key tags are listed below in a sample INCAR file (Note: As with many other VASP files, the INCAR file directions can be line-dependent. To illustrate this in the sample, the line number is enclosed in parentheses, but should not be included in an actual INCAR file).
(1)SYSTEM = KVO3 initial calculations
(4) ISTART = 0 ! this is a new job
(5) ICHARG = 2 ! charge density: from overlapping atoms
(6) ENCUT = 952 ! cutoff energy, in eV
(7) NELM = 25 ! maximum of 25 electronic steps (SCF cycles)
(8) NELMIN = 2 ! minimum of two steps
(9) EDIFF = 10E-8 ! accuracy for electronic minimization
(10) PREC = Normal ! normal precision
(11) LREAL = Auto ! real space projection yes/no
Making the KPOINTS File
Last, but not least is the KPOINTS file. As its name suggests, this file is responsible for generating/directing the k-points which are used in the calculation. This file is in fact the simplest of the files which have to be made. A sample, with important strings and tags is below (Note: As with many other VASP files, the KPOINTS file directions are in most cases line-dependent. To illustrate this in the sample, the line number is enclosed in parentheses, but should not be included in an actual KPOINTS file).
(2) 0 !This indicats the k-points will be determined from an automatic generation of the mesh.
(3) Monkhorst-Pack !This will place the k-points using the Monkhorst-Pack grid
(4) 2 2 2 ! This specifies the number of divisions in each reciprocal vector which makes up the k-point grid, thus determining the number of k-points.
This type of KPOINTS file should suffice for most work.