Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
(triangle symbols), 
(circle symbols), and 
(square symbols).
The switching barrier for a 3 × 3 × 3 supercell of a perfect bulk is also given for comparison (star symbols).
