# Cubic EoS - only VAPOR root is converging o_o

1. ### maistral

88
Hello. I would like to inquire as to how to deal with the said topic title.

I'm trying to generate a VLE graph for ethylene oxide-water. While I know that EO will quickly vaporize since the boiling point of EO is quite low, I'm still trying to generate a VLE using SRK.

So while the vapor root is converging, the liquid root won't.

Upon inspection (and using taylor expansion of the third degree to simplify the equation), I noticed that the two roots (the liquid root and the useless middle root) converge in the complex domain. Does this have a physical meaning?