Structure and dynamics of water–smectite interfaces: Hydrogen bonding and the origin of the sharp O–Dw/O–Hw infrared band

from molecular simulationsSupplementary information

Marek Szczerba, Artur Kuligiewicz, Arkadiusz Derkowski, Vassilis Gionis, Georgios D. Chryssikos, and Andrey G. Kalinichev

Three short simulations for beid05_Na in the following ensembles were performed:

NVT, with all oxygen atoms having LJ parameters of 0.1554 kcal/mol (D0) and 3.8 Å (R0);

NPT, with all oxygen atoms having modified LJ parameters; and

NPT with LJ parameters modified only for surface oxygens.

The results are presented in Table S1.

Table S1. Optimized dimensions of the simulation cell (Å).

Direction NVT NPT R0 (all OB) = 3.8 NPT R0 (surface OB) = 3.8

a 41.47 44.10 43.57

b 35.92 38.30 37.92

c 30.58 31.10 30.92

In the case of NVT a small deformation of the tetrahedral sheet was found (Figure S1).

Figure S1. Final frame after 200 ps of NVT (300 K) simulation. Deformations of the tetrahedral sheet are

marked with black circles.

An increase in a and b directions for both NPT simulations is visible; in NPT with all oxygen

atoms having modified LJ parameters the increase was ~6.5%. Deformation of octahedral Al

atoms and also some tetrahedral sheet deformation were also evident, however (Figure S2).

Figure S2. Final frame after 200 ps of NPT (300 K, 1 atm) simulation with all OB atoms with D0 =

0.1554 kcal/mol and R0 = 3.8 Å (R0). Substantial deformation of the octahedral sheet is visible. Deformation of

tetrahedral sheet is also observed.

In the case of NPT with only surface oxygen modified, with increase of the LJ R0 parameter

an increase in the simulation cell but no distortions were observed (Figure S3).

Figure S3. Final frame after 200 ps of NPT (300 K, 1 atm) simulation with only surface OB atoms with D0 =

0.1554 kcal/mol and R0 = 3.8 Å (R0). LJ parameters for other atoms taken from CLAYFF (Cygan et al., 2004).

In addition, the NPT simulations with modified LJ parameters for surface oxygens and also

for tetrahedral Si and tetrahedral Al atoms were performed. The parameters of the AT and ST

were modified to compensate for the increased size of the surface bridging oxygens. Applying

the usual arithmetic mixing rules for the parameters of interatomic interactions gives the R0

value of 3.4596 Å (in CLAYFF it is 3.7064 Å).

The results presented in Table S2 demonstrate a decrease in simulation-cell dimensions

toward those values of NVT simulation. The values are still greater, however, than the

experimental values, indicating that other parameters should be modified in order to describe

properly the interaction of clay minerals with water and the structure.Table S2. Optimized dimensions of the simulation cell (Å) after introducing modification of surface oxygens and

tetrahedral Si and Al atoms.

DirectionAT, ST R0 parameter (Å)

3.4596 3.3674 3.1429

a 42.95 42.75 42.47

b 37.30 37.15 36.98

c 30.78 30.84 30.73

The value of 3.4596 corresponds to a compensated increased size of the surface oxygens

considering only the ST–OB distance. This does not take into account that increased LJ

parameters for OB lead to repulsion of oxygen atoms. The final frame of the simulation is

presented in Figure S4.

Figure S4. Final frame after 200 ps of NPT (300 K, 1 atm) simulation with only surface OB atoms with R0 =

3.8 Å and tetrahedral Si and tetrahedral Al R0 = 3.4596 Å.

A further decrease in this parameter leads to small a decrease in the symmetry of the

hexagonal cavity (Figure S5). The decrease of sigma to 3.03 leads to complete destruction of

the structure.

Figure S5. Final frame after 200 ps of NPT (300 K, 1 atm) simulation with only surface OB atoms with R0 =

3.8 Å and tetrahedral Si and tetrahedral Al R0 = 3.1429 Å. A decrease in symmetry of the cavities leading to the

ditrigonal shape is clearly visible.