How to create input files?

Input-file preparation dialogue box creates files in the order of Structure–>K-points–>Potential–>Instructions, which in the case of VASP translates to the order POSCAR–>KPOINTs–>POTCAR–>INCAR.

  1. Structure:

  • CINEMAS can create a structure file from the scratch by taking symmetry and site information, or load structure files from several formats such as .xsf(XCrysden), .vasp(VASP), .in(Quantum Espresso), .cif and etc. Generation of a structure from the scratch is performed using spglib, while cif format is handled using pymatgen libraries.

  • Once symmetry/site data or a file-form-disk is exported, further atomic sites can be added or deleted or degree-of-freedom for structural relaxation can be restricted(the same can be done from structure manager side as well).

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Fig. 112 Input-files: Creating structure from the scratch by supplying symmetry/site information(an example of SrTiO3 for spacegroup \(Pm\bar{3}m\) with no. 221).

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Fig. 113 Input-files: Exporting the information and generating full structure of SrTiO3.

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Fig. 114 Input-files: Restrict degree of freedom by selecting ‘selective dynamics’ at the left bottom, and check the boxes to restrict the atom.

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Fig. 115 Input-files: Alternatively load structure file from different formats.

  1. K-points:

From the second tab, K-points file can be created in two modes: either in automatic or band-structure mode. Automatic mode is self-explanatory, while for the band-structure mode, using icon Brillouin zone for any loaded structure can be visualized, k-path be selected and corresponding co-ordinates are exported and K-points file is created. In the current version of CINEMAS, only high symmetry points are exported and labeling has to be done manually.

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Fig. 116 Input-files: Creating K-points for standard calculations.

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Fig. 117 Input-files: Create K-points for band-structure calculations.

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Fig. 118 Input-files: For band-structure, visualize BZ and select k-path and export corresponding co-ordinates. In current version labeling of high-symmetry points has be done manually.

  1. Potentials:

From the third tab, type of potential(LDA/GGA-PW91/GGA-PBE) can be chosen as well as available option of potentials with different valence. Above holds true if potential files have been configured already.

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Fig. 119 Input-files: Select potentials for respective atomic species.

  1. Instructions:

From the fourth tab, instructions-file(INCAR for VASP) can be prepared, essentially telling DFT-engine(VASP) what to do. CINEMAS can prepare instruction-file in graphical, as well as text mode. All possible code-specific tags have been divided into several categories to help a user lesser experienced with the DFT-code. These categories are further distributed over different user levels such as basic/intermediate/expert. Alternatively expert users can directly type the file in text mode. Additionally any other instruction file can be loaded and modified, or saved for repetitive use in future.

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Fig. 120 Input-files: Select categories from the left pane, as per nature of the calculation.

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Fig. 121 Input-files: Expanded view of a category(here Relaxation).

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Fig. 122 Input-files: Further expand any category based upon user level, by clicking advance options.

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Fig. 123 Input-files: Hovering the cursor on a particular option, shows relevant tag for DFT-code(VASP here).

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Fig. 124 Input-files: A sample view of few options selected.

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Fig. 125 Input-files: Text mode equivalent of previous window, after selecting options.