Interatomic Potential for Hydrocarbons on the Basis of the Modified Embedded-Atom Method with Bond Order (MEAM-BO)
This paper describes the new development of the modified embedded atom method (MEAM) potential that includes bond order (MEAM-BO). This method is intended to describe the energy levels of unsaturated hydrocarbons as well as saturated hydrocarbons. Parameters including bond lengths, bond angles, and atomization energies at 0 K, dimer molecule interactions, rotational barriers, and the pressure−volume-temperature relationships of dense systems of small molecules are included in this model. This gives a comparable or more accurate property relative to experimental and first-principles data than the classical reactive force fields REBO and ReaxFF used to look at the nanoscale of polymer materials. This extension of the MEAM potential for unsaturated hydrocarbons (MEAM-BO) is a necessary and critical step toward developing more reliable and accurate polymer simulations with their associated structure−property relationships, such as reactive multicomponent organic/metal) systems, polymer−metal interfaces, and nanocomposites.
This new formalism for bond order (MEAM-BO) was preceded by including 3NN interactions into the C diamond cubic reference state and enabling more accurate predictions of diamond cubic properties. Prior models resulted in outputs where the diamond cubic C was not the lowest energy crystal structure. The potential optimization for saturated bonds and unsaturated bonds were consecutively performed with reference to a modest database of atomization energies, bond distances, and bond angles of select molecules, the potential energy curves of H2, CH4, C2H2, C2H4, benzene, graphene, (H2)2, (CH4)2, (C2H6)2, and (C3H8)2, diamond properties/energies of the different carbon phases, and the pressure−volume−temperature (PVT) relationship of dense molecular systems.
These properties calculated using the new MEAM potential (without bond order) were compared with the associated experimental data, first principles calculations, the previous MEAM potential, and two other reactive potentials, REBO and ReaxFF. The MEAM-BO results show that the properties of saturated and unsaturated hydrocarbons are comparable to those of the other reactive potentials and are reasonably close to the experimental data/first-principles calculations. The new MEAM-BO potential can easily be combined with literature MEAM potentials for many other elements, enabling computation of properties of a wide variety of multicomponent systems.
Sungkwang Mun,† Andrew L. Bowman,† Sasan Nouranian,‡ Steven R. Gwaltney,§ Michael I. Baskes,*,∥,⊥,#,∇ and Mark F. Horstemeyer†,○
† Center for Advanced Vehicular Systems (CAVS), Mississippi State University, Mississippi State, Mississippi 39762, United States ‡ Department of Chemical Engineering, The University of Mississippi, University, Mississippi 38677, United States § Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762, United States ∥ Department of Aerospace Engineering, Mississippi State University, Mississippi State, Mississippi 39762, United States ⊥ Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
- Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California 92093, United States
∇ Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, United States ○ Department of Mechanical Engineering, Mississippi State University, Mississippi State, Mississippi 39762, United States
Since interatomic potentials are at the heart of atomistic and molecular simulations, the advancement of materials diversity and computational interest has growingly translated into more sophisticated potentials that can provide accurate descriptions between different constituent elements’ atomic interactions. These interactions provide the basis for the calculation of material properties of interest. The situation has escalated even more with a growing scientific and technological interest in alloys and composite/multilayer materials that are made of two or more constituent elements. The interface between dissimilar materials introduces a whole new set of fundamental scientific problems that need to be solved. Currently, interfacial and interphase engineering are at the forefront of scientific research in different disciplines within automotive, aerospace, military, and biomedical industries.1−6 researchers need to tackle many hitherto unresolved scientific issues related to molecular mechanisms involved in the observed macroscopic material properties; as a consequence, establishing fundamental composition−microstructure−property relationships is a critical need. However, a scientific gap exists today, wherein interatomic potentials that can reliably and accurately reproduce and predict the myriad of properties associated with complex single- and multicomponent, multielement material systems are nonexistent or are available with limited applicability. The current work’s significance is the development of an extensive interatomic potential based on a promising modified embedded atom method (MEAM) formalism.7 The MEAM potential is a modification to the original embedded-atom method (EAM), developed by Daw and Baskes8 in 1984, that includes a formalism for covalent materials (directional bonding), such as silicon and silicon−germanium alloys. Both EAM and MEAM potentials are widely used by computational materials scientists and engineers conducting atomistic simulations related to point defects, melting, alloying, grain boundary structure and energy, dislocations, twins, segregation, fracture, surface structure, epitaxial growth, bulk and interface problems (surface phonons), and interdiffusion in metallic alloys. The unique feature of MEAM is its ability to reproduce the physical properties of a large number of crystal structures in unary, binary, ternary, and higher order metal systems with the same formalism. The recent development9 by the authors shows MEAM successfully extended to saturated hydrocarbons without any modification to the original formalism, which gives a possibility to study multielement systems based the vast parameter database of metals. As a continuation of the previous work of Nouranian et al.,9 we developed here a new formalism for unsaturated bond energies and added to the existing MEAM formalism. Furthermore, we improved the results of previous works that are not related to bond order through the following: (1) a critical issue in the carbon (C) parameters of the previous work has been fixed so that the diamond cubic structure (reference structure for C) is energetically more stable than the face-centered cubic (FCC) and body-centered cubic (BCC) crystal structures; (2) partial contributions of third nearest neighbor (3NN) interactions10 are considered in the C reference structure, which allows for more accurate diamond properties than those predicted by the previous parameters; (3) the reference structure for CH has been changed from the CH dimer to methane, which improves the agreement with the hydrocarbons experimental data.