nt between models and photometric data; however, to reproduce the effective temperature of stars with different masses in different evolutionary phases, an ad hoc value of the mixing length parameter should be adopted, as suggested by observations [see e.g., @chieffi95; @morel00; @ferraro06; @yildiz07; @gennaro11; @piau11; @bonaca12] and detailed hydrodynamical simulations [see e.g., @ludwig99; @trampedach07].

The main goal of this paper is to re-examine the old lithium problem in light of the improvements in the adopted physical inputs and observational data and to perform a quantitative analysis of the uncertainties affecting surface lithium depletion during the pre-MS phase. The aim is to compute, by means of updated models, theoretical error bars to be applied to the comparison between predictions and data available for stars in young open cluster and binary systems, as partially done in earlier other works [see e.g., @dantona84; @swenson94; @ventura98; @piau02; @sestito06].

The paper is structured in the following way. Section \[sec:data\] presents the adopted $^7$Li data sample for the selected open clusters, followed by a brief description of present models (Sect. \[sec:models\]). In Sect. \[sec:error\] we evaluate the main theoretical uncertainties affecting surface lithium abundance. Finally, in Sect. \[sec:results\], the comparison between predicted and observed lithium abundances for both young open clusters and binary systems is discussed.

Lithium data {#sec:data}
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Surface $^7$Li abundances for young open clusters are taken from the homogeneous database made available by @sestito05. Here, we focus our analysis on clusters younger than about 150 - 200 Myr, in order to avoid MS depletion effects [see e.g., @sestito05], with different metallicities for which a significant number of data in a wide range of effective temperatures are available. The clusters that satisfy these criteria are, Ic 2602, $\alpha$ Per, Blanco 1, Pleiades, and Ngc 2516.

Lithium abundances for young double-lined ec