Author Topic: Issue with the forcefield  (Read 151 times)

sridhar

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Issue with the forcefield
« on: September 19, 2018, 02:12:25 PM »
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

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Re: Issue with the forcefield
« Reply #1 on: September 20, 2018, 09:23:48 AM »
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

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Re: Issue with the forcefield
« Reply #2 on: September 21, 2018, 07:18:44 AM »
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

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Re: Issue with the forcefield
« Reply #3 on: September 21, 2018, 04:44:04 PM »
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.