This interface appear when you click on the Solver Options button 
from the The Rigorous PS Calculation Toolbox Dialog. From this interface the user can specify numerical solver options, such as numerical tolerances and other calculation method options that are described below.
● Uknown Variable Tolerance: The tolerance of the numerical solver. The numerical solver considers that convergence has been achieved when the maximum variable correction between two successive iterations is less than this (relative) tolerance.
● Rediduals Tolerance: The tolerance of the additional convergence constraint imposed by SuperPro. Convergence is assumed successful if the maximum residual of the objective function is be lower than this value.
● Bubble/Dew Point V/L Threshold: The value of the vapor mole flow (V) or liquid mole flow (L) fraction for bubble (V = Threshold) and dew (L = Threshold) point calculations.
● Rachford-Rice Zero Threshold: Threshold to infer if a mixture is in the 2-phase region or not by calculating the value of the Rachford-Rice function (RR) at the limits 0 and 1. A mixture is assumed to be 100% in the liquid phase if RR(0) > threshold. A mixture is assumed to be 100% in the vapor phase if RR(1) < -threshold. This threshold does not apply in the case that the negative flash concept flag has been selected.
● Negative Flash Concept: When this flag is selected the negative flash concept (Whitson and Michelsen, 1989) is applied to the flash solution algorithm. The program will infer if a mixture is in the 2-phase region by the calculated vapor fraction. The computational efficiency of the solution is increased because the solver does not evaluate the Rachford-Rice function at the limits 0 and 1.
● K-values as External Loop (for non-ideal VLE cases): By checking this option, K-values will be used as the external loop instead of molar fractions.
● Ideal Solution as Guess: With this option selected, the solver will use the solution of the corresponding ideal VLE problem (Raoult’s Law for the calculation of K-values) in non-ideal VLE cases.
● Flash Point Calculations for Vapor Fraction Initial Guess: The solution algorithm will use an initial guess for the vapor fraction based on the calculations of the Rachford-Rice function at the bubble, due and middle point (vapor fraction = 0.5).
Curtis H. Whitson and Michael L. Michelsen (1989) The Negative Flash, Fluid Phase Equillibria, 53, 51-71.