Mutation Selection test FMutSel0-M0 (Null) FMutSel-M0 (Alternative) df=0, how to do Chi square test?

Question

[kabir.deb]

Hello Experts,

I am doing Mutation Selection test FMutSel0-M0 (Null) FMutSel-M0 (Alternative) of my test data set because of its AT richness, however, np for both models is coming same, 5. Therefore degrees of freedom become 0. In this scenario how can I do the Chi-square test. Some literature said that "within FMutSel and the Chi-square distribution cannot be used to compare them. However, the use of the Akaike information criterion" leads to clear preference of FMutSel over all old models" Yang and Nielsen 2008. So my question is how to do AIC in this context.

Thanks in advance