System Tab
----------------

The first step in performing simulations with the GUI is defining the system.  The layout of the system tab is shown below:



.. image:: system.*
   :align: center


**Grid**:  
The upper left frame contains inputs for the user-defined grid.  The dimensionality of the system is inferred from the grid entries: entering a grid for the x-axis only implies a 1-d system.  Adding a grid for the y-axis implies a 2-d system, etc.  

**Materials**:  
The middle-top frame contains the entries for the bulk material properties.  Multiple materials can be added to the system.  Their location is specified in the ``Location`` field.  

**View system**:  
Provides a depiction of the system geometry, including the x and y meshes, different materials regions, and the planar defects (grain boundaries).

**Planar Defects**:  
Planar defects are added in the middle-bottom frame.  For a 1-d system, a planar defect location is specified by 1 point.  For a 2-d system, a planar defect is specified by 2 points.  The energy level of the defect (with respect to the intrinsic energy level), the defect density, capture cross sections, and charge states are specified here.

**Illumination**
Specify the illumination on the system.  Options are 1. monochromatic, with user-defined wavelength and power, and 2. 1 sun illumination, where the spectral density is taken from https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html (Direct+circumsolar spectrum).

**Absorption**
Specify the material absorption.  Options are 1. a user-defined single absorption coefficient, and 2. loading in absorption spectrum from an external file.  Tutorial2 has a sample absorption file.  Note that the format of the file is assumed to be two column, with first column containing wavelength of light in units of [nm], and the second column containing the associated absorption coefficient in units of [1/m].

**Generation Rate**:  
The carrier generation rate density is entered in the lower-left frame.  There is an option to vary 1 parameter in this profile.  In cases where the generation profile changes, the parameter which is varied must be specified in the field ``parameter name``.  If the generation profile does not change, this field may be left blank.