The core Coulomb potential in OpenMX is replaced by a tractable norm-conserving pseudopotential proposed by Morrison, Bylander, and Kleinman , which is a norm-conserving version of the ultrasoft pseudopotential by Vanderbilt . Although the pseudopotentials can be generated using ADPACK which is a program package for atomic density functional calculations and available from a website (http://www.openmx-square.org/), for your convenience, we offer a database (http://www.openmx-square.org/) of the pseudopotentials as the database Ver. 2019. If you want to use pseudopotentials stored in the database, then copy them to the directory, 'openmx3.9/DFT_DATA19/VPS/', while most of data have been already copied in the distributed package of OpenMX Ver. 3.9. You can freely utilize these data, but we cannot offer any warranty on these data. The assignation of pseudopotentials can be made using a keyword 'Definition.of.Atomic.Species' as in the case of specification of basis functions as follows:
<Definition.of.Atomic.Species H H6.0-s2p1 H_CA19 C C6.0-s2p2 C_CA19 Definition.of.Atomic.Species>The pseudopotential file can be specified in the third column, and the file must be existing in the directory 'DFT_DATA19/VPS'. In the specification of atomic coordinates, it is required to give the number of electrons for up- and down-spin states for each atom as follows:
<Atoms.SpeciesAndCoordinates 1 C 0.000000 0.000000 0.000000 2.0 2.0 2 H -0.889981 -0.629312 0.000000 0.5 0.5 3 H 0.000000 0.629312 -0.889981 0.5 0.5 4 H 0.000000 0.629312 0.889981 0.5 0.5 5 H 0.889981 -0.629312 0.000000 0.5 0.5 Atoms.SpeciesAndCoordinates>where the sixth and seventh columns give the number of initial charges for up and down spin states for each atom, respectively. The sum of up and down charges for the atomic element should be equivalent to the number of electrons which is taken into account in the pseudopotential generation. Then, the proper number for each pseudopotential can be found in the pseudopotential file '*.vps'. For example, you will see the following line in the file 'C_PBE19.vps' for carbon atom in the database Ver. 2019.
valence.electron 4.0000The number '4.0' corresponds to the number of electrons which is taken into account in the pseudopotential generation. So, we see in the above example that the sum of up (2.0) and down (2.0) spins charges is 4.0 for 'C' in the specification of 'Atoms.SpeciesAndCoordinates'. In Tables 2 and 1 we show the number of valence electrons in the pseudopotentials provided as the database Ver. 2019.
When you make pseudopotentials using ADPACK by yourself, you should pay attention to the following points.
You will find the further details in the manual of the program package 'ADPACK'. However, it is noted that generation of good pseudopotentials requires considerable experiences more than what we think at the beginning.