2.4 MD simulation details
The potential parameters and models of the concentrated
H2SO4 and C4 reactants for MD
simulations were from the same as our previous
work.6,7 The C4 reactants model includes equivalent
2-butene and isobutane with size of 6.0×6.0×4.0 nm3.
The size of H2SO4 model is 6.0×6.0×8.0
nm3, containing 2848
H2SO4 molecules, 84 hydronium ions, and
84 bisulphate ions. For the interfacial model, the sandwich-like models
were constructed with pure H2SO4 model
in the middle and pure C4 reactants model in the both sides. 2 nm gap
between pure H2SO4 model and pure C4
reactants model was used to place DESs. The number of ChCl-Pho (1:2) in
the gap are 6, 15, and 24, corresponding to the concentration of 1.0
wt%, 3.0 wt%, and 5.0 wt%, respectively. For ChCl-TsOH (1:1), the
number is 6, 16, and 26, respectively. For ChCl-BOA (1:2), the number is
6, 12, and 21, respectively. Initially, the energy minimization of 5000
steps was carried out, followed by 8 ns canonical (NVT )
simulations at 298.2 K with nose-hoover thermostat. The
isothermal-isobaric (NPT ) ensemble was further conducted for 10
ns to fully equilibrate configures. During the simulation, the number
density distribution of each moiety was calculated every 2 ns, and the
configures were fully equilibrated after there are no apparent
deviations for the density. At last, 6 ns NVT was carried out for
data collection of interest with the time steps of 2.0 fs. The
semi-isotropic Parrinello Rahman barostat method on z axis was
used with 2.0 ps relaxation time at 1 bar for all the NPTensemble to keep the interface unchanged15.
For all the MD simulations, GROMACS software was employed with periodic
boundary conditions (PBC) in three dimensions36. The
Lennard-Jones interaction and Coulombic interaction were cut off at 1.2
nm. All the covalent bonds related to hydrogen atoms were treated using
the LINCS algorithm. Maxwell distribution was employed to obtain the
initial atomic velocity. The particle grid Ewald method was used to
treat long-range electrostatic interactions. The OPLS-AA was used to
treat the interaction between the DESs,
H2SO4 and C4
hydrocarbons6,7,29. At the same time, the charges of
the DESs were refitted based on the ChelpG method at the Basis set of
6-311++G(d,p) level with Gaussian 09 program37.