As an example of the cluster case, using an input file 'Fe_Cluster_jx.dat' which is stored in the directory 'work', you can first perform a conventional calculation using 'openmx' as
% mpirun np 2 ./openmx Fe_Cluster_jx.datThe input file 'Fe_Cluster_jx.dat' is for the SCF calculation of a iron dimer. After finishing the calculation normally, you can obtain a scfout file 'Fe_Cluster_jx.scfout'. Then the calculation by 'jx' is performed as
% ./jx Fe_Cluster_jx.scfout jx_cluster.configwhere 'jx_cluster.config' is also available in the directory 'work'. Then, you may see the following message on your screen.
******************************************************************** ******************************************************************** jx: code for calculating an effective exchange coupling constant J Copyright (C), 2003, Myung Joon Han, Jaejun Yu, and Taisuke Ozaki 2019, Asako Terasawa and Taisuke Ozaki This is free software, and you are welcome to redistribute it under the constitution of the GNUGPL. ******************************************************************** ******************************************************************** Read the scfout file (Fe_Cluster_jx.scfout) *** The file format of the SCFOUT file: 3 And it supports the following functions:  jx  polB  kSpin  Z2FH  calB *** Previous eigenvalue solver = Cluster atomnum = 2 ChemP = 0.089740215968 (Hartree) E_Temp = 300.000000000000 (K) Evaluation of J based on cluster calculation i j J [meV] J [mRy]  1 1 1591.520791120630 116.974621661729 1 2 106.511867492210 7.828477938772 2 2 1591.520746009061 116.974618346089 Elapsed time = 0.036225 (s)The exchange coupling constant between atoms 1 and 2 is calculated to be 106.5 meV.
As an example of the bulk case, you can perform a conventional calculation using 'openmx' and an input file 'Fe_Bulk_jx.dat' available in the directory 'work' as
% mpirun np 28 ./openmx Fe_Bulk_jx.datThe input file 'Fe_Bulk_jx.dat' is for the SCF calculation of a BCC iron. After finishing the calculation normally, you can obtain a scfout file 'Fe_Bulk_jx.scfout'. Then the calculation by 'jx' is performed as
% mpirun np 112 ./jx Fe_Bulk_jx.scfout Fe_Bulk_jx.config  tee jx.logwhere 'Fe_Bulk_jx.config' is available in the directory 'work'. Then, you may see the following message on your screen.
******************************************************************** ******************************************************************** jx: code for calculating an effective exchange coupling constant J Copyright (C), 2003, Myung Joon Han, Jaejun Yu, and Taisuke Ozaki 2019, Asako Terasawa and Taisuke Ozaki This is free software, and you are welcome to redistribute it under the constitution of the GNUGPL. ******************************************************************** ******************************************************************** Read the scfout file (Fe_Bulk_jx.scfout) *** The file format of the SCFOUT file: 3 And it supports the following functions:  jx  polB  kSpin  Z2FH  calB *** Previous eigenvalue solver = Band atomnum = 2 ChemP = 0.205912787451 (Hartree) E_Temp = 300.000000000000 (K) Jij calculation for a periodic structure Number of kgrids: 27 27 27 flag_periodic_sum = 0: coupling between site i at cell 0 and site j at cell R Number of poles of FermiDirac continued fraction (PRB.75.035123): 60 i j c1 c2 c3 J [meV] J [mRy] time_eig [s] ...  ... 1 1 2 2 2 0.845809571401 0.062165857439 0.51534 ... 1 1 2 2 1 0.274300677331 0.020160728111 0.00000 ... 1 1 2 2 0 0.036006012552 0.002646393135 0.00000 ... 1 1 2 2 1 0.274300705154 0.020160730156 0.00000 ... 1 1 2 2 2 0.845809596417 0.062165859278 0.00000 ... 1 1 2 1 2 0.274300737539 0.020160732536 0.00000 ... 1 1 2 1 1 0.206315672897 0.015163922403 0.00000 ... 1 1 2 1 0 0.149714301525 0.011003798302 0.00000 ... 1 1 2 1 1 0.206315540488 0.015163912672 0.00000 ... 1 1 2 1 2 0.274300804604 0.020160737465 0.00000 ... ... .. 2 2 0 1 2 0.149714016159 0.011003777328 0.00000 ... 2 2 0 0 2 0.401809366424 0.029532443987 0.00000 ... 2 2 0 0 1 11.452192349598 0.841720620155 0.00000 ... Elapsed time = 340.817975 (s)In Fig. 38 (a), the obtained exchange coupling constant for the bcc Fe is plotted as a function of distance as well as cases of (b) hcp Co, (c) fcc Ni, and (d) Fe dimer. In all the calculations, basis sets of A6.0Hs2p2d2 (A=Fe, Ni, Co), exchange correlation functions of GGAPBE, and ferromagnetic spin configurations are adopted. The input files used for the calculations are Fe_Bulk_jx.(dat,config), Co_Bulk_jx.(dat,config), Ni_Bulk_jx.(dat,config), and Fe_Cluster_jx.(dat,config) which are all available in the directory 'work'. The details of the calculations can be found in Ref. [19].
It is also possible to calculate the Curie temperature of periodic systems from calculated exchange coupling constants and the mean field approximation. That is, the Curie temperature of general periodic system can be obtained as the maximum eigenvalue of the following eigenvalue equation:
Here, the definitions of and are found in Eqs. (5) and (8), respectively. Table 8 shows the calculated Curie temperature by Eq. (9) for the bcc Fe, hcp Co, and fcc Ni together with the experimental values.

