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The moving components of combustion engines are operated under harsh conditions of high pressures and temperatures. Extreme‐pressure anti‐wear additives, such as tricresyl phosphate (TCP), are mixed with base oil to prevent wear through the formation of a lubricant film on the substrate. We studied the effect of liquid pressure on the decomposition pathway of TCP in base oil molecules (2,5‐dimethylhexane) using hybrid quantum‐classical simulations with density functional theory for electrons. At a temperature of 300 K, we found that: (i) bond‐breaking barrier energies of both the OC and PO bonds of TCP decrease monotonically as the liquid pressure increases; (ii) the bond‐breaking barrier energy of PO is lower than that of OC at pressures of 0 and 2.0 GPa, but is higher at a pressure of 5.0 GPa; and (iii) the applied pressure significantly lowers the bond‐breaking barrier energies of both OC and PO when the PO bond of TCP is directed upward from the substrate. These findings are explained by the inhomogeneous distribution of base oil molecules around TCP and the steric repulsion of the PO bond of TCP. These results indicate that the internal structures of the lubricant films are pressure‐dependent. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, we have determined key properties of Ar and Ne in bcc W that relate to the possible bubble formation of implanted Ar and Ne atoms. The most stable interstitial site of Ar/Ne in bcc W is the tetrahedral site, as in the case of H and He. An interstitial atom causes the substantial strain of surrounding W atoms and the low electron-density region. The calculated migration energy of both Ar and Ne is very small, less than 0.2 eV of H. We calculated the binding energies of nearby interstitial atoms and found a strong dependence of atomic species. The attractive interaction between Ne atoms is the largest. Owing to such a small migration energy and a significant interaction between Ar/Ne atoms, interstitial atoms can act as traps for additional atoms and tend to form clusters in the absence of previous damage such as vacancies. The results presented here can explain the possible clustering of implanted atoms in bcc W via self-trapping. [ABSTRACT FROM AUTHOR]