The loss of magnetic pressure accompanying the decay of the magnetic field in a magnetar may trigger exothermic electron captures by nuclei in the shallow layers of the outer crust. The threshold density and pressure, as well as the maximum amount of heat that can be possibly released were calculated for different nuclei. The Landau-Rabi quantization of electron motion was taken into account using approximate analytical formulas. Results were obtained using experimental atomic masses and the \(Q_\beta\) values (included recommended ones) from the 2016 Atomic Mass Evaluation supplemented with the atomic mass model HFB-24 available on the BRUSLIB database. Each file contains data for electron captures by nuclei with the specified charge number Z and mass number A. The columns are as follows: magnetic field strengh in units of \(B_{\rm rel}=\dfrac{m_e^2 c^3}{e \hbar}\approx 4.41\times 10^{13}\, \rm G\) the pressure in dyn cm-2 the mass density in g cm-3 the heat per nucleon in MeV. The files with (without) label 'ex' contain results for ground state to excited state (ground state) transitions.

This work was financially supported by Fonds de la Recherche Scientifique - FNRS (Belgium) under grant No. IISN 4.4502.19. This work was also partially supported by the European Cooperation in Science and Technology Action CA16214 and the CNRS International Research Project (IRP) ``Origine des éléments lourds dans l'univers: Astres Compacts et Nucléosynthèse (ACNu)''.