BasicChemistryModel<psiReactionThermo>& chemistry = pChemistry();
scalar dtChem = refCast<const BasicChemistryModel<psiReactionThermo>>
(
    chemistry
).deltaTChem()[0];
basicSpecieMixture& composition = thermo.composition();
PtrList<volScalarField>& Y = composition.Y();
volScalarField& p = thermo.p();