Statistical Analysis of Tri-Cresyl Phosphate Conversion on an Iron Oxide Surface Using Reactive Molecular Dynamics Simulations

Abstract

Parallel reactive molecular dynamics simulations were used to statistically analyze chemical reactions between tri-cresyl phosphate (TCP) and an amorphous iron oxide surface. To accurately model this system, a new parameter set for Fe/P/O interactions within the ReaxFF framework was developed. Using the new parameter set, 100 parallel simulations of a single TCP molecule on an amorphous iron oxide surface were run to capture multiple possible reactions at temperatures ranging from 300 to 700 K. The frequency of TCPsurface reactions for each atom type and each unique reaction site on the TCP was analyzed across the range of temperatures. Finally, the composition of the material chemisorbed to the surface was determined and compared to results from previously reported experimental measurements of TCP films in oxygen deficient environments. The results are specifically relevant to TCP, but the parallel reactive simulation approach and statistical analysis of reaction sites can be applied more generally to a range of chemical systems, particularly those involving complex molecules and disordered surfaces where many different reactions are possible.

Substituent Effects on the Thermal Decomposition of Phosphate Esters on Ferrous Surfaces

“…51 Velocity Verlet integration was used with a time step of 0.25 fs. 36 The bottom atomic layer of the substrate was frozen, and periodic boundary conditions were applied in the x and y directions. The temperature was controlled using a Nosé-Hoover thermostat 52,53 with a damping parameter of 25 fs, which was applied to all non-frozen atoms.…”

“…All of the MD simulations used the same ReaxFF parameters for C/H/O/Fe/P interactions as were employed by Khajeh et al 36 ReaxFF is a bond order-based force field that was originally developed by van Duin et al 33 to study the dissociation and reactions of small hydrocarbon molecules. The version of ReaxFF implemented in LAMMPS uses the functional form which was outlined by Chenoweth et al 54 and was fully described by Aktulga et al 55 The general form of ReaxFF is given by: 35…”

“…35 The point charges on the atoms vary dynamically during the MD simulation and are calculated using the charge equilibration (Qeq) method. [55][56][57] In the ReaxFF parameter file used in the current study (see Supporting Information), the Fe/P/O ReaxFF parameters were developed by Khajeh et al 36 The (within 4 %), 39 and Fe3O4 (within 3 %). 58 They have also been shown to perform favourably compared to other many-body force fields in describing the mechanical properties of α-Fe.…”

“…Cr2O3 in the presence of FeS2. 67 The ReaxFF parameter set has previously been applied to study the thermal decomposition of TCP on a-Fe3O4-OH surfaces 36 as well as TCP interactions with nanodiamonds on the same surface. 37…”

“…ReaxFF compared to DFT, as has been noted in previous comparisons of polar molecules on metal surfaces. 82 These observations indicate that, although the adsorption energy is generally overestimated compared to DFT, the ReaxFF parameterisation 36 can describe the chemisorption interactions between phosphate esters (both intact and dissociated) and ferrous surfaces. Moreover, the energy differences between the intact and dissociated molecules are in good agreement, as shown in Fig.…”