Issue with the forcefield

[sridhar]

Hi Prof. Dubbeldam,

I'm using raspa for hydrogen adsorption simulation in ZIF-8, I had edited the input file and  force field file of MOF-5 given in the examples for the using ZIF-8 (lennard jones parameters are also changed according to ZIF-8) as adsorbate . After running the simulation i got high adsorption capacities of hydrogen than reported in literature, it happened for 77K and 300K. I would like to know what might be the problem in this simulation.

[b]My input file [/b]
SimulationType                MonteCarlo
NumberOfCycles                50000
NumberOfInitializationCycles  1000
PrintEvery                    2000

Forcefield                    GenericMOFs1

Framework 0
FrameworkName ZIF-8
UnitCells 1 1 1 
HeliumVoidFraction 0.484279
ExternalTemperature 300 
ExternalPressure   5e5 10e5 15e5 20e5 30e5 40e5 50e5 60e5 10e6 20e6

Component 0 MoleculeName             H2
            MoleculeDefinition       TraPPE
            TranslationProbability   1
            ReinsertionProbability   1
            SwapProbability          1
            CreateNumberOfMolecules  0


I edited only forcefield mixing.def file and left forcefield and psuedo atoms.def file as it is

Edited force field is
# general rule for shifted vs truncated
shifted
# general rule tailcorrections
no
# number of defined interactions
55
# type interaction, parameters.    IMPORTANT: define shortest matches first, so that more specific ones overwrites these
O_             lennard-jones    30.19     3.12
N_             lennard-jones    34.72    3.26256
C_             lennard-jones    52.84    3.4299
F_             lennard-jones    36.4834   3.0932
B_             lennard-jones    47.8058   3.58141
P_             lennard-jones   161.03     3.69723
S_             lennard-jones   173.107    3.59032
Cl_            lennard-jones   142.562    3.51932
Br_            lennard-jones   186.191    3.51905
H_             lennard-jones    22.14     2.57
Zn_            lennard-jones    62.3992   2.46155
Be_            lennard-jones    42.7736   2.44552
Cr_            lennard-jones     7.54829  2.69319
Fe_            lennard-jones     6.54185  2.5943
Mn_            lennard-jones     6.54185  2.63795
Cu_            lennard-jones     2.5161   3.11369
Co_            lennard-jones     7.04507  2.55866
Ga_            lennard-jones   208.836    3.90481
Ti_            lennard-jones     8.55473  2.8286
Sc_            lennard-jones     9.56117  2.93551
V_             lennard-jones     8.05151  2.80099
Ni_            lennard-jones     7.54829  2.52481
Zr_            lennard-jones    34.7221   2.78317
Mg_            lennard-jones    55.8574   2.69141
Ne_            lennard-jones    21.1352   2.88918
Ag_            lennard-jones    18.1159   2.80455
In_            lennard-jones   301.428    3.97608
Cd_            lennard-jones   114.734    2.53728
Sb_            lennard-jones   225.946    3.93777
Te_            lennard-jones   200.281    3.98232
Al_            lennard-Jones   155.998    3.91105
Si_            lennard-Jones   155.998    3.80414
He             lennard-jones    10.9      2.64
CH4_sp3        lennard-jones    148     3.73
CH3_sp3        lennard-jones    108.0     3.76
CH2_sp3        lennard-jones    56.0      3.96
CH_sp3         lennard-jones    17.0      4.67
C_sp3          lennard-jones     0.8      6.38
H_com          lennard-jones    30        2.58
H_h2           lennard-jones    36.7      2.59   
O_co2          lennard-jones    79.0      3.05
C_co2          lennard-jones    27.0      2.80
C_benz         lennard-jones    30.70     3.60
H_benz         lennard-jones    25.45     2.36
N_n2           lennard-jones    36.0      3.31
N_com          none
Ow             lennard-jones    89.633    3.097
N_dmf          lennard-jones    80.0      3.2
Co_dmf         lennard-jones    50.0      3.7
Cm_dmf         lennard-jones    80.0      3.8
O_dmf          lennard-jones    100.0     2.96
H_dmf          lennard-jones    8.0       2.2
Ar             lennard-jones    119.8     3.34
Kr             lennard-jones    166.4     3.636
Xe             lennard-jones    221.0     4.1
# general mixing rule for Lennard-Jones
Lorentz-Berthelot


Thanks.

[David Dubbeldam]

Higher adsorption capacity compared to what? experiments? other simulations?
For the first, you need to make sure you use a reliable force field and a structure that corresponds to the experiments (taking inaccessibility for example into account). For the latter, you need to make sure you do the simulations exactly as published in the literature.

[sridhar]

Thanks for the reply,

I compared with the experiments and i want to make sure my force fields and input file are correct because in the warnings of each simulation it shows max 50 interactions are missing which are Eg: Zn_H_O, C1_C2_Zn etc.

Near 77K in the literature mentioned that quantum effects are considered to get accurate experimental results. Is it possible to include that in raspa?

[David Dubbeldam]

The forcefield and molecules present in RASPA are examples. For your system you need to define your own force field (for the adsorbate, the ZIF-8, and the cross-interactions). All relevant interactions needs to be defined.