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The strength of metals as a function of temperature is still not very well understood, even in the case where thermal overcoming of obstacles by dislocations is believed not to be superimposed by other temperature dependent effects, like solute atom diffusion. Our simulation calculations offer a means to close some of the gaps in understanding, as they exclude both superimposed effects of any kind as well as errors due to non-ideal experimental conditions. In this contribution our results concerning the activation enthalpy and -volume for obstacles of atomic size are presented. The simulations reveal that for equivalent conditions an obstacle field can well be compared to an equidistant obstacle arrangement to be overcome. Another simplification of the activation model can be done by replacing this obstacle row by a continuous obstacle wall without affecting the activation parameters. From this it has to be concluded that the activation volume does not always depend on the obstacle spacing due to first principles. A length L is introduced which for a concrete obstacle spacing determines the number of obstacles to be overcome simultaneously for thermal activation. Calculations on obstacle fields show that for solute atom concentrations between 0.1% and 20%, this length L rather than the obstacle spacing controls thermal activation.