## Visualizing iso-surfaces¶

Iso-surfaces from data in a cube-file or a gpw-file can be visualized using Mayavi from the command line like shown here.

It’s a good idea to create a short alias like this:

$alias iso="python3 -m ase.visualize.mlab -C gpaw"  so that you can simply do: $ iso CO.cube  # plot cube file
$iso slab-4.gpw # plot electron density from gpw-file$ iso slab-4.gpw -n 15  # plot wave function from gpw-file
$iso -h # help!  ## Making x-y plots¶ If you want to plot an x-y plot from data in a csv-file (comma separated values), you can use gnuplot: $ gnuplot
gnuplot> plot "abc.csv" using 1:2


Alternatively, use this little Python script:

import sys
import numpy as np
import matplotlib.pyplot as plt
for filename in sys.argv[1:]:
x = a
for y in a[1:]:
plt.plot(x, y, '-')
plt.show()

\$ python3 <path-to-script>/xy.py abc.csv


## Writing 3-d data to cube files¶

This can be done from Python using the ase.io.write() function:

from ase.io import write
write('abc.cube', atoms, data=data)


## Square root¶

Square roots are calculated like this: 2**0.5 or sqrt(2) (the sqrt function must first be imported: from math import sqrt or from numpy import sqrt).

## Integer division¶

In Python, / is used for both integer- and float divisions. Integer division is only performed if both sides of the operator are integers (you can always force an integer division by using //):

>>> 1 / 3
0
>>> 1 / 3.0
0.33333333333333331


## Why does changing one variable change another one?¶

The = operator in Python is not and assignment operator, it is a naming operator: It makes a new name for (reference to) the object:

a = [1, 2, 3, 4, 5]  # Create a list
b = a                # New name for list
a = 42
print(b)             # [1, 2, 42, 4, 5]

c = 7
d = c
c += 42   # d is still 7, we just did
# c = c + 42
# creating a new object 49 and
# giving it the name c


## Saving plots¶

You can save plots made with matplotlib by pressing the floppy-disk icon in the bottom of the plot, and save as a .png file.

You can save a picture of the atoms from ASE’s GUI by choosing Save, and then specify a .png file.

You can view .png files in the databar with the command eog (“eye of Gnome”).