Top panel: coefficients obtained for the six different models described in Sect. 5.2 as a function of the irradiation temperature for planets with different gravities and an internal temperature of 100 K. TiO and VO have been artificially removed from the atmosphere. Bottom panel: mean relative difference between the numerical and the analytical model for the six different models described in Sect. 5.2. The first line is the mean difference for 10^-4bar <P< 10^-2bar, the second line for 10^-2bar <P< 10⁰bar and the third line for 10⁰bar <P< 10²bar. In terms of Rosseland optical depth, the low pressure zone corresponds to the optically thin part of the atmosphere with 10^-8 (25 ms^-2/ g) ≲ τ_R ≲ 10^-2 (25 ms^-2/ g). The medium pressure zone corresponds to the transition from optically thin to optically thick with 10^-4 (25 ms^-2/ g) ≲ τ_R ≲ 10 (25 ms^-2/ g). The high pressure zone corresponds to the optically thick part of the atmosphere with (25 ms^-2/ g) ≲ τ_R ≲ 10⁴ (25 ms^-2/ g).