Equation Of State (EOS)

Equation Of State (EOS)#

We have designed the Equation Of State (EOS) workflow to automate the computation needed to fit the equation of state for bulk systems. Starting from an approximate lattice constant, it is performed a bulk calculation (single-point energy) for different lattice constants.
The equilibrium volume, bulk modulus and equilibrium energy of the structure model are derived from one selected formula. For example, the Murnaghan EOS can be used as the relationship between the volume of a body and the pressure to which it is exposed. It is one of the many state equations used to model the behaviour of matter under high-pressure conditions.
A EOS project starts with the definition of the atomic structure. We refer the user to section Structure Modeling in ASAP for further information on ASAP structure builder/viewer interface.
After the atomic structure is defined, edit the type of project by selecting Equation of State from the list of possible project types implemented in ASAP.
Workflow eos select
Workflow eos select project type

Then click on the Parameters icon to open the Equation of State parameters widget.

Workflow eos param select
Workflow eos param widget

The project parameters that can be tuned are:

  • Number of images. The different configurations are created by interpolating the initial and final volume.

  • Lattice constant variation (%). Parameter to select the volume range.

To compute the Equation of State, a series of single-point calculations are performed. Click on the Calculator icon to select the computational engine used for those single-point calculations.

Workflow eos calc select
We refer the user to chapter Calculators for further information on ASAP available calculators.
Click on the Run icon to open the Run widget. Then click on the Run button to execute the Equation of State workflow.
Workflow eos run select
Workflow eos run widget
We refer the user to chapter Runners for further information on computational resources configuration in ASAP.
After the EOS workflow is started, the Run widget shows the energy of each of the single-point calculations being part of the EOS workflow.
Workflow eos run output calc

After the calculation is completed, click on the Exit and analyse button to open the analysis widget.

Equation Of State workflow: Analysis#

Workflow eos run exit analyse

You can also open the EOS analysis widget by selecting the Analyse icon associated with a completed project.

Workflow eos analyse select
Workflow eos analyse widget
In the left panel of the EOS analysis widget, the figure shows the energy of each of the single-point calculations represented as a function of the crystal volume. You can select different formulas for fitting the data.
Workflow eos analyse method
The equilibrium volume, bulk modulus and equilibrium energy of the structure model are derived from the selected formula.
The right panel of the EOS analysis widget shows information of the crystal unit cell.
Workflow eos analyse unit cell