`compute_gkma`

¶

The `compute_gkma`

keyword can be used to calculate the modal heat current using the Green-Kubo modal analysis (GKMA) method [Lv2016].
The results are written to the heatmode.out output file.

## Syntax¶

```
compute_gkma <sample_interval> <first_mode> <last_mode> <bin_option> <size>
```

`sample_interval`

is the sampling interval (in number of steps) used to compute the heat modal heat current.

`first_mode`

and `last_mode`

are the first and last mode, respectively, in the eigenvector.in input file to include in the calculation.

`bin_option`

determines which binning technique to use.
The options are `bin_size`

and `f_bin_size`

.

`size`

defines how the modes are added to each bin.
If `bin_option`

is `bin_size`

, then this is an integer describing how many modes are included per bin.
If `bin_option`

= `f_bin_size`

, then binning is by frequency and this is a float describing the bin size in THz.

## Examples¶

### Example 1¶

```
compute_gkma 10 1 27216 f_bin_size 1.0
```

This means that

you want to calculate the modal heat current with the GKMA method

the modal heat flux will be sampled every 10 steps

the range of modes you want to include of calculations are from 1 to 27216

you want to bin the modes by frequency with a bin size of 1 THz

### Example 2¶

```
compute_gkma 10 1 27216 bin_size 1
```

This example is identical to Example 1, except the modes are binned by count. Here, each bin only has one mode (i.e., all modes are included in the output).

### Example 3¶

```
compute_gkma 10 1 27216 bin_size 10
```

This example is identical to Example 2, except each bin has 10 modes.

## Caveats¶

This computation can be very memory intensive. The memory requirements are comparable to the size of the eigenvector.in input file.

Depending on the number of steps to run, sampling interval, and number of bins, the heatmode.out output file can become very large as well (i.e., many GBs).

This keyword cannot be used in the same run as the compute_hnema keyword. The keyword that appears last will be used in the run.