National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow, Russia:

M. A. Fedina, Engineer, e-mail: zara.91@mail.ru

Aalto University School of Science, Espoo, Finland:
M. G. Ganchenkova, Assistant Professor1, Visiting Researcher

The values of energy parameters of point defects in tungsten, forecasted by numerous published first-principle calculations, have a noticeable spread, causing an appropriate doubt in their reliability. Incorrect selection of calculation parameters can be only one possible reason for this situation. This inaccuracy leads to further errors in the study of microstructure evolution under the influence of different factors, such as in current urgent problem of tungsten behavior studying, when it will be used as the material for ITER divertor. On the example of the simplest point defects (mono- and divacancy, hydrogen atom), there was carried out a systematic study of the sensitivity of calculated energy parameters of defects to the choice of basic calculation parameters. On the basis of the potential energy calculations, there were found such ideal crystal parameters as lattice parameter, bulk modulus, vacancy formation energy, divacancy formation energy, and solution energy of hydrogen atoms in tetrahedral and octahedral sites. The carried out research has shown that provision of reasonable accuracy of the calculations for tungsten sets rather severe restrictions on minimum allowable values of calculation input parameters, such as choice for integration mesh of first Brillouin zone, and choice of supercell size, which was not observed in many earlier published works. According to this, detailed preliminary convergence tests of acceptable accuracy of calculation results become more significant.

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