Home Page for the Environment-Dependent Interatomic Potential

Martin Z. Bazant


The Environment-Dependent Interatomic Potential (EDIP) is an efficient and realistic model for interatomic forces in covalent solids and liquids which incorporates recent theoretical advances in understanding the environment-dependence of (sigma) chemical bonding in condensed phases [1,2]. The parameterization for silicon [3] significantly outperforms other existing potentials for silicon, including the popular Stillinger-Weber and Tersoff potentials, when tested for bulk phases (amorphous, liquid, crystal elasticity, thermal expansion,...), defects (point defects, stacking faults, dislocations,...) and phase transitions (crystal phases -- amorphous -- liquid). EDIP has been used to study the liquid-amorphous transition, self-diffusion, crystal platicity, brittle fracture, solid phase epitaxial growth, amorphous structures, vibrational spectra, and much more. Recently, EDIP has also been extended by N. A. Marks to carbon by incorporating the effects of pi-bonding empirically [Phys. Rev. B. (2001). postscript].

Free software and Usage Agreement

Since it is a non-trivial task to efficiently and accurately compute forces with a many-body potential like EDIP, tested and optimized subroutines for force computation (written in C by Martin Bazant and translated into fortran by Noam Bernstein in 1997, then further optimized by Xianglong Yuan in 2002) are provided below, which may be incorporated into any molecular dynamics program. Documentation within the source code explains the interface, which takes as input the positions of the atoms and a Verlet neighbor list for the interaction topology and returns as output the forces, effective coordinations, energies and virial. By separating various contributions to the virial, it is straighforward to compute the stress tensor as well.

These subroutines are available at no cost to facilitate the application and testing of EDIP. If the subroutines are used in published research, however, it is with the understanding that the theoretical work and empirical fitting which led to the potential will be properly acknowledged. In particular, the following three publications should be cited at once and in order:

  1. M. Z. Bazant and E. Kaxiras, Phys. Rev. Lett. 77, 4370 (1996).
  2. M. Z. Bazant, E. Kaxiras, J. F. Justo, Phys. Rev. B 56, 8542 (1997).
  3. J. F. Justo, M. Z. Bazant, E. Kaxiras, V. V. Bulatov, and S. Yip, Phys. Rev. B 58, 2539 (1998).

More detailed descriptions of the theory behind EDIP and the algorithm for force computation can be found in: M. Z. Bazant, Interatomic Forces in Covalent Solids, Ph.D. Thesis in Physics, Harvard University (1997). (However, the thesis was written before the final parameter set was obtained!)

Software Available to Download

  1. EDIP Subroutines: These are the original subroutines which have been available since 1997 and tested extensively by many users.

    In April 2002, Xiaolong Yuan somewhat further optimize the force calculation, yielding a typical performance boost of roughly 5% (before any compiler optimization). The following two patched subroutines are recommended:

    Other versions are also available along with a detailed description of the patches.

    After you download the subroutines, please take a minute to send an email giving your name, affiliation, address and a brief description of how you plan to use EDIP. This information will be added to the database of researchers using EDIP worldwide (which was automatically generated on the old server).

  2. Complete Parallel MD Package: Stefan Goedecker has incorporated EDIP into a freely available, user-friendly MD program written in fortran90. The subroutine for EDIP force calculation translated into fortran90 is also available separately.

  3. Conjugate-Gradient Energy Minimization Code: Joao Justo, one of the original developers of EDIP, has an optimized conjugate-gradient code using EDIP which is available upon request: jjusto@lme.usp.br.

Additional References

As the body of literature using EDIP grows, the following list of subsequent pulications (not only by Bazant) on applications and extensions of the potential will eventually be maintained at this web site. Please come again. If you would like to add papers and/or links to this list, please send an email.

EDIP for Silicon

  1. M. Z. Bazant, E. Kaxiras and J. F. Justo, The Environment-Dependent Interatomic Potential applied to silicon disordered structures and phase transitions, Mat. Res. Soc. Proc. 491, 339 (1997).
  2. M. de Koning, A. Antonelli, M. Z. Bazant, E. Kaxiras and J. F. Justo, Finite temperature molecular-dynamics study of unstable stacking fault energies in silicon, Phys. Rev. B 58 , 12555 (1998). (e-print)
  3. N. Bernstein, M. J. Aziz, and E. Kaxiras, Atomistic simulations of solid-phase epitaxial growth in silicon, Phys. Rev. B 61, 6696 (2000).
  4. S. M. Nakhmanson and D. A. Drabold, Computer simulation of low-energy excitations in amorphous silicon with voids, J. Non-crystalline Solids 266-269, 156 (2000).
  5. L. Brambilla, L. Colombo, V. Rosato, and F. Cleri, Solid-melt interface velocity and diffusivity in laser-melt amorphous silicon, Appl. Phys. Lett. 77, 2337 (2000).
  6. P. Keblinski, M. Z. Bazant, J. Dash, and M. Treacy, Thermodynamic behavior of a model covalent material described by the Environment-Dependent Interatomic Potential, Phys. Rev. B 66, 4104 (2002). (e-print)
  7. M. Maki-Jaskari, K. Kaski, and A. Kuronen, Simulations of crack initiation in silicon.
  8. M. Bazant and E. Kaxiras, On the structure of amorphous silicon and its surfaces.
  9. J. Nord, K. Nordlund, and J. Keinonen, Amorphization mechanism and defect stuctures in ion beam amorphized Si, Ge, and GaAs.

EDIP for Carbon

  1. N. A. Marks, Phys. Rev. B. 63, 0635401 (2001).

Inversion Methods

  1. M. Z. Bazant and E. Kaxiras, Modeling covalent bonding in solids by inversion of cohesive energy curves, Phys. Rev. Lett. 77, 4370 (1996). ( e-print)
  2. M. Z. Bazant and B. Trout, A method to extract intermolecular potentials from the temperature dependence of Langmuir curves, Physica A 300, 137-173 (2001). (e-print).

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