Inaccurate thermochemistry for species ionically bonded with potassium

[CMDePompa]

Hi! I am trying to get thermochemistry for some species that are ionically bonded to potassium. For now, I am comparing calculations for KCN, KOH, and K2SO4 with their experimental data in JANAF tables to verify potassium is accurately treated in the calculations. Unfortunately, the Arkane calculated enthalpies are nowhere near correct, and consequently, neither are the Gibbs free energy calculations. The Cp and S values are pretty close to experimental data. Might anyone have any insight into this problem?

[JacksonBurns]

I think @rwest can probably speak to this the best, but my understanding is that RMG doesn't handle ions (see here), so perhaps Arkane is in the same boat?

[CMDePompa]

Thanks for getting back to me. I made a change to /rmg/RMG-database/input/quantum_corrections/data.py at line 48, the atom_hf value for potassium atom to match the value from JANAF. I also added a library index for potassium atom to the main thermo library at /rmg/RMG-database/input/thermo/libraries/primaryThermoLibrary.py:

entry(
    index=47,
    label="K",
    molecule="""
multiplicity 2
1 K u1 p0 c0
""",
    thermo=ThermoData(
        Tdata=([0, 100, 200, 250, 298.15, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1039.54, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, 2600, 2700, 2800, 2900, 3000, 3100, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, 4100, 4200, 4300, 4400, 4500, 4600, 4700, 4800, 4900, 5000, 5100, 5200, 5300, 5400, 5500, 5600, 5700, 5800, 5900, 6000
], "K"),
        Cpdata=([0, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96797323135755, 4.96821223709369, 4.96869024856597, 4.96964627151052, 4.97155831739962, 4.97466539196941, 4.97992351816444, 4.98757170172084, 4.99856596558317, 5.01314531548757, 5.03250478011472, 5.05664435946463, 5.0862810707457, 5.12213193116635, 5.16395793499044, 5.21247609942639, 5.2684034416826, 5.33150095602294, 5.40272466539197, 5.48183556405354, 5.57026768642447, 5.66778202676864, 5.76553537284895, 5.87930210325048, 6.00071701720841, 6.13432122370937, 6.27868068833652, 6.434034416826, 6.6008604206501, 6.77461759082218, 6.96080305927342, 7.16108986615679, 7.37284894837476, 7.44383365200765, 7.64890057361377, 7.86137667304015, 8.07050669216061, 8.23709369024857, 8.45721797323136, 8.68044933078394, 8.9060707456979, 9.13288718929254, 9.36018164435946, 9.58675908221797, 9.81166347992352, 10.0334608030593, 10.1522466539197, 10.3577915869981, 10.557361376673, 10.75
], "cal/(mol*K)"),
        H298=(21.27, "kcal/mol"),
        S298=(38.322, "cal/(mol*K)"),
    ),
    shortDesc="""library value for reference potassium""",
    longDesc="""

""",
)

My advisor and I decided we needed the atom specifically due to the nature of the enthalpy calculations. There is JANAF data for K+ in the gas phase. I will try putting that in as well to see if maybe that is the source of error.

Thanks again for the help!