mirror of https://github.com/abinit/abinit.git
100 lines
4.4 KiB
Markdown
100 lines
4.4 KiB
Markdown
---
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description: How to build an input file for a ground state calculation
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authors: FJ
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---
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<!--- This is the source file for this topics. Can be edited. -->
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This page gives hints on how to build an input file for a ground state calculation with the ABINIT package.
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## Introduction
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The computation of the ground state energy of an assembly of nuclei and
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electrons placed in a repeated cell can be done using (1) plane waves and
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norm-conserving pseudopotentials, or, (2) so-called "Projector-Augmented
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Waves" (PAW method), with appropriate pseudoatomic data, or (3) wavelets. The
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wavelet framework is described [[topic:Wavelets|here]].
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In the plane wave framework, the program admits many different types of
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pseudopotentials. There are several complete sets of norm-conserving
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pseudopotentials available for most elements of the periodic table.
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The recommended tables (GGA-PBE, GGA-PBEsol and LDA) come from the |pseudodojo| project
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with ONCVPSP pseudopotentials ([[cite:Hamann2013]])
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both in scalar-relativistic format and fully-relativistic version with spin-orbit coupling.
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For PAW calculation,the recommended one (GGA-PBE and LDA) is the JTH
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table in the PAW XML format ([[cite:Jollet2014]]).
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The choice between norm-conserving
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pseudopotentials or PAW is deduced automatically by the choice of the
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pseudopotential in the "files" file. An input file must specify the following items:
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* the [[topic:crystal|crystalline structure and symmetries]]
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* the set of [[topic:k-points|k-points]] used
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* the [[topic:xc|exchange and correlation functional]]
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* the convergence settings
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* possibly [[topic:PAW|PAW]] special settings
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* possibly, input variables for [[topic:spinpolarisation|spin-polarized systems and spin orbit coupling]] calculations.
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An example of a minimal input file to calculate the ground state of crystalline aluminium is given here:
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```
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# Crystalline aluminum. Calculation of the total energy
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# at fixed number of k points and broadening.
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#Definition of occupation numbers
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occopt 4
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tsmear 0.05
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#Definition of the unit cell
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acell 3*7.60 # This is equivalent to 7.60 7.60 7.60
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rprim 0.0 0.5 0.5 # FCC primitive vectors (to be scaled by acell)
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0.5 0.0 0.5
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0.5 0.5 0.0
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#Definition of the atom types
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ntypat 1 # There is only one type of atom
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znucl 13 # The keyword "znucl" refers to the atomic number of the
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# possible type(s) of atom. The pseudopotential(s)
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# mentioned in the "files" file must correspond
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# to the type(s) of atom. Here, the only type is Aluminum
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#Definition of the atoms
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natom 1 # There is only one atom per cell
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typat 1 # This atom is of type 1, that is, Aluminum
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xred 0.0 0.0 0.0 # This keyword indicate that the location of the atoms
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# will follow, one triplet of number for each atom
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# Triplet giving the REDUCED coordinate of atom 1.
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#Definition of the planewave basis set
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ecut 6.0 # Maximal kinetic energy cut-off, in Hartree
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pawecutdg 10.0 #Maximal kinetic energy cut-off, in Hartree for the fine grid in case of PAW calculation
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#Definition of the k-point grid
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ngkpt 2 2 2 # This is a 2x2x2 FCC grid, based on the primitive vectors
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chksymbreak 0
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#Definition of the SCF procedure
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nstep 10 # Maximal number of SCF cycles
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toldfe 1.0d-6 # Will stop when, twice in a row, the difference
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# between two consecutive evaluations of total energy
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# differ by less than toldfe (in Hartree)
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# This value is way too large for most realistic studies of materials
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```
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## Related Input Variables
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{{ related_variables }}
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## Selected Input Files
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{{ selected_input_files }}
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## Tutorials
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* [[tutorial:base1|The tutorial 1]] deals with the H2 molecule: get the total energy, the electronic energies, the charge density, the bond length, the atomisation energy
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* [[tutorial:base2|The tutorial 2]] deals again with the H2 molecule: convergence studies, LDA versus GGA
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* [[tutorial:base3|The tutorial 3]] deals with crystalline silicon (an insulator): the definition of a k-point grid, the smearing of the cut-off energy, the computation of a band structure, and again, convergence studies ...
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* [[tutorial:base4|The tutorial 4]]] deals with crystalline aluminum (a metal), and its surface: occupation numbers, smearing the Fermi-Dirac distribution, the surface energy, and again, convergence studies ...
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