Simulation of elastic constant of Si (diamond lattice)

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This projects illustrates the use of LAMMPS for simulation of elastic constant of Si (diamond lattice) at absolute zero temperature.

Elastic constants characterize the stiffness of a material. The formal definition is provided by the linear relation that holds between the stress and strain tensors in the limit of infinitesimal deformation. In tensor notation, this is expressed as s_ij = C_ijkl * e_kl, where the repeated indices imply summation. s_ij are the elements of the symmetric stress tensor. e_kl are the elements of the symmetric strain tensor. C_ijkl are the elements of the fourth rank tensor of elastic constants. In three dimensions, this tensor has 3^4=81 elements. Using Voigt notation, the tensor can be written as a 6x6 matrix, where C_ij is now the derivative of s_i w.r.t. e_j. Because s_i is itself a derivative w.r.t. e_i, it follows that C_ij is also symmetric, with at most 7*6/2 = 21 distinct elements.

At zero temperature, it is easy to estimate these derivatives by deforming the simulation box in one of the six directions using the change_box command and measuring the change in the stress tensor. A general-purpose script that does this is given in the examples/elastic directory described in this section.

Model New Results

Software Used

LAMMPS

LAMMPSlogo.png

LAMMPS is a classical molecular dynamics code, and an acronym for Large-scale Atomic/Molecular Massively Parallel Simulator.

LAMMPS has potentials for solid-state materials (metals, semiconductors) and soft matter (biomolecules, polymers) and coarse-grained or mesoscopic systems. It can be used to model atoms or, more generically, as a parallel particle simulator at the atomic, meso, or continuum scale.

LAMMPS runs on single processors or in parallel using message-passing techniques and a spatial-decomposition of the simulation domain. Many of its models have versions that provide accelerated performance on CPUs, GPUs, and Intel Xeon Phis.



Using LAMMPS on Kogence

Using LAMMPS on Kogence

You can either fork and modify an existing LAMMPS public project or alternatively you can also start from scratch and create a new LAMMPS project.

  • In order to fork an existing project
    • Make sure you fist click "Copy" button to create a personal copy to modify.
    • Then click Settings -> Machine to choose a machine and
    • Click Settings -> Software and choose LAMMPS from the dropdown menu. In the empty text box, type the name of the input script.
  • In order to create a new project from scratch
    • Click on Model Library -> My Models
    • Click on + button on top left corner. Provide name and short description for your new project.
    • Click on + button again in the next project screen and either create or upload an existing LAMMPS input file.
    • Click Settings -> Software and choose LAMMPS from the dropdown menu. In the empty text box, type the name of the input script.
  • Access to command terminal with installed LAMPPS environment
    • Click Settings -> Software and choose LAMMPS from the dropdown menu. In the empty text box, type "xterm" (without quotes).

To see detailed step-by-step instructions on how to use LAMMPS on Kogence free cloud supercomputing platform [click here].

LAMMPS Versions on Kogence

  • 11 Aug, 2017 (runs with only MPI threads and no openMP threads even on single node)
  • 31 Mar, 2017 (runs with openMP threads on single node)

For more details see LAMMPS .