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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Difference in Molar Enthalpies between EoS and DFT","articleBody":"`Contributions.IdealGas` uses different methods for EoS and DFT (see below). \r\n\r\nJoback gives very small values for the `IdealGas` molar enthalpy (as fat as I tested all in the range ~1e-13 * JOULE). \r\n\r\n\r\n```python \r\nimport numpy as np\r\n\r\nfrom feos.si import *\r\nfrom feos.pcsaft import *\r\n\r\nfrom feos.eos import EquationOfState, Contributions\r\nfrom feos.eos import State as EosState\r\nfrom feos.eos import PhaseEquilibrium as EosPhaseEquilibrium\r\n\r\nfrom feos.dft import HelmholtzEnergyFunctional, PhaseEquilibrium\r\nfrom feos.dft import State as DftState\r\nfrom feos.dft import PhaseEquilibrium as DftPhaseEquilibrium\r\n\r\nsubstances = ['nitrogen', 'methane']\r\nparams = PcSaftParameters.from_json(substances=substances, pure_path='pure_parameters.json', binary_path='binary_parameters.json', search_option=IdentifierOption.Name)\r\n\r\neos = EquationOfState.pcsaft(params)\r\ndft = HelmholtzEnergyFunctional.pcsaft(params)\r\n\r\nvle_eos = EosPhaseEquilibrium.bubble_point(eos, temperature_or_pressure=110*KELVIN, liquid_molefracs=np.array([0.1, 0.9]))\r\nvle_dft = DftPhaseEquilibrium.bubble_point(dft, temperature_or_pressure=110*KELVIN, liquid_molefracs=np.array([0.1, 0.9]))\r\n\r\nprint(vle_eos.liquid.helmholtz_energy_contributions()) # Gives QSPR as IdealGas contribution\r\nprint(vle_dft.liquid.helmholtz_energy_contributions()) # Gives Joback as IdealGas contribution\r\n\r\nprint(vle_eos.liquid.molar_enthalpy(contributions=Contributions.ResidualNvt) - vle_dft.liquid.molar_enthalpy(contributions=Contributions.ResidualNvt)) #Gives very good agreement in the ResidualNvt contribution\r\n\r\nprint(vle_eos.liquid.molar_enthalpy(contributions=Contributions.IdealGas) - vle_dft.liquid.molar_enthalpy(contributions=Contributions.IdealGas)) # Gives large discrepancy in IdealGas contribution\r\n```\r\n","author":{"url":"https://github.com/RolfStierle","@type":"Person","name":"RolfStierle"},"datePublished":"2022-11-08T15:11:04.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/68/feos/issues/68"}