Water molecules were represented using the SPC model.59
The particle-mesh Ewald summation (PME) method60 was
used for the electrostatic interactions with a real space cutoff of
1.0 nm and a reciprocal grid of 60 × 60 × 60 cells with a fourthorder
B-spline interpolation. For van der Waals interactions, we
used a cutoff distance of 1.0 nm. All MD simulations were
performed by using the GROMACS package (version 4.0.5).61
Prior to actual simulations, the systems were energy
minimized and equilibrated by short 20 ns MD runs. The
production simulations were performed over a period of 200 ns
for each AuNP. For comparison, previous simulation studies of
related systems covered time scales of the order of 1 ns.29 The
time step was set to 1 fs, and the neighbor list (cutoff 1.0 nm)
was updated for every frame. The simulations were performed
both in the NVT and NPT ensembles for 200 ns, respectively.
For the NVT ensemble, the temperature was set to 310 K using
the Berendsen thermostat62 with a time constant of 0.1 ps. In
addition, for the NPT ensemble, the Berendsen algorithm62
with a compressibility of 4.5 × 10−5 bar−1, time constant of 5
ps, and reference pressure of 1 bar was used for isotropic
pressure coupling. The variable cell size in NPT resulted in
0.02−0.03 nm changes in the simulation box dimensions (7.06
nm). However, most of the analysis was performed using the