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The positional derivatives of the two ion interactions in equation (139) has to be evaluated in order to calculate the exchange striction. Within the McPhase package the program makenn may perform this task and it will use analytical formulas. Here comes a typical code example:
REM create exchange interaction call makenn 7 -rkky -3 1.2 call copy results/makenn.j mcphas.j REM ... and its position derivatives using the -djd... option of makenn call makenn 7 -rkky -3 1.2 -djdx call makenn 7 -rkky -3 1.2 -djdy call makenn 7 -rkky -3 1.2 -djdz call copy results/makenn.djdx mcphas.djdx call copy results/makenn.djdy mcphas.djdy call copy results/makenn.djdz mcphas.djdz REM ... and optional add also some explicit strain dependencies REM (in case of RKKY coming from the strain dependence of the Fermi Wave Vector kf) call makenn 7 -rkky -3 1.2 -djdeps1 call makenn 7 -rkky -3 1.2 -djdeps2 call makenn 7 -rkky -3 1.2 -djdeps3 call makenn 7 -rkky -3 1.2 -djdeps4 call makenn 7 -rkky -3 1.2 -djdeps5 call makenn 7 -rkky -3 1.2 -djdeps6 call copy results/makenn.djdx mcphas.djdeps1 call copy results/makenn.djdy mcphas.djdeps2 call copy results/makenn.djdz mcphas.djdeps3 call copy results/makenn.djdx mcphas.djdeps4 call copy results/makenn.djdy mcphas.djdeps5 call copy results/makenn.djdz mcphas.djdeps6 REM start mcphase with option -doeps to calculate strain call mcphasit -doeps