Downloading, Installing and an Introduction to QUANTUM ESPRESSO

Quantum Espresso is an integrated suite of Open-Source computer codes for electronic-structure calculations and materials modelling at the nanoscale. It is based on density-functional theory, plane waves, and pseudopotentials.

Though it can be used on Linux, Mac and Windows, in this post I will show you how to install and use it on Linux- UBUNTU.

Downloading:

Go to this link and download the package, or download it using the terminal by giving the following command.
sudo apt-get install quantum-espresso (You can skip step 1 if you install it this way)

Installing:

Step 1:

To use Quantum Espresso, you need to extract(uncompress) the zip/tar(compressed) file that you downloaded(You don’t need to uncompress it if you used the install command).

To do that just right click on the compressed file, and select ‘Extract’.

Or you can do it using the terminal by using the following command:
tar -zxvf espresso-5.0.2.tar.gz
NOTE: Make sure you write the correct file name and versionespresso-5.0.2.tar.gz. It will probably be different for you.

Once installation is done, a directory will be created with many files and other directories.

Step 2:

Now an important thing to note is that the Quantum Espresso needs a working fortran-95 compiler (most “fortran-90” compilers are ok, “g77” is not). If you don’t have it installed, the rest of the steps may not work. You can try performing the next step, if it works then you are good to go, else you need a Fortran compiler.

You can download and install a Fortran compiler by executing the following command in the terminal:

sudo apt-get install gfortran

Step 3:

Once, you have done the installation, you need to change your directory to the directory of the Quantum Espresso software, and run the following terminal command:

./configure
You can change the directory by using the command cd so if your copy of Quantum Espresso is in a directory called ‘qe-6.1’ which is in the Home directory, then you can use: cd qe-6.1

“configure” is a wrapper, calling the “install/configure” script, that tries to guess your machine and to choose compilation and linking options accordingly. “install/configure” is generated from “install/configure.ac” using the complex but well-known Unix utility “autoconf”. The result of “configure” is a file called “make.sys” containing the compilation and linking options. You may want to have a look at it to verify what “configure” thinks about your system. Several options to “configure” may (and sometimes, have to) be specified (see below).
If you get a message “architecture xxx not recognized”, specify option “ARCH=…”, such as e.g. (for a BlueGene machine):
./configure ARCH=ppc64-bg
If “configure” selects a compiler you don’t like (or one that doesn’t like Quantum ESPRESSO) specify option “F90=…” or “MPIF90=…”, e.g.:
./configure F90=gfortran
If everything is fine you should get a bunch of (mostly obscure and irrelevant) messages but no error. Read the last lines: you may need to understand them if something goes wrong at compilation stage, or if you need to boost performances.

Once this is done, you can compile the packages you will be needing. If you need to perform Plane Wave SCF calculation then you need to compile the ‘pw’ package. To do that run the following command:

make pw
“make” is another complex but standard unix utility that compiles what is needed in the way it is needed and in the order in which is needed (in Fortran-90 you need to compile modules before programs that use them, for instance). The configuration files for “make” are either coming with the package or are generated by “configure”. If everything goes well, executables will appear in “bin/”:
ls bin/*.x

You can compile all the available packages at once by running:

make all

Step 4:

Once you’re done with the above steps, it means you now have the necessary tools to perform a pw scf calculation.
To perform such a calculation, you need an input file for Quantum Espresso. You can download the sample input file from this link. Once you have the file, save it in a directory of your choice. For the sake of this tutorial, let’s say you save it in a directory called ‘QE’ inside the Quantum Espresso installation directory.

Now, create a directory called ‘temp’ inside the directory that contains the input file(in our example the directory is ‘QE’).

Now let me tell you a little about the input file that we have here. In this file, we are basically trying to find out some of the properties for a Cu atom, like the total energy, etc.

The input file is a really important file and you will need to learn quite a few things to be able to build one yourself.
There are a lot of things that need explaining there, but I guess I will leave that for another post, and in this tutorial we will, just focus on running our first pw scf calculation. For the sake of the tutorial you can download the input file that I will be using from here or you can just copy the following and save it in a file called in.
&control prefix='' outdir='temp' pseudo_dir = '.', / &system ibrav= 2, celldm(1) =6.824, nat= 1, ntyp= 1, ecutwfc =30.0, occupations='smearing', smearing='mp', degauss=0.06 / &electrons / ATOMIC_SPECIES Cu 63.546 Cu.pbesol-dn-kjpaw_psl.0.2.UPF ATOMIC_POSITIONS Cu 0.00 0.00 0.00 K_POINTS automatic 8 8 8 0 0 0

Step 5:

Now the last thing you need to do is to get the pseudopotential for your atom.
If you open the input file using a text editor, you will notice the field: pseudo_dir = ‘ ‘, inside the &control section.

Inside the single quotes you need to specify the directory of your pseudopotential. But before that you first need to download one from here. Once you go to the link you can click on any atom to get a list of it’s available pseudopotentials. For this tutorial, we need a particular potential for Cu. So click on Cu(29) in the periodic table shown. Now you will see a list of a variety of potentials. Just search for this one : ‘Cu.pbesol-dn-kjpaw_psl.0.2.UPF’ and download it.

Step 6:

'/home/manas/qe-6.1/bin/pw.x' <in>out

Once the execution is done, you will notice a file named out created in the directory with the input file.
Open and you can find information regarding the energies, how many iterations it took to converge, and more.

References and more Resources on Quantum Espresso:

Manas Sharma

PhD researcher at Friedrich-Schiller University Jena, Germany. I'm a physicist specializing in theoretical, computational and experimental condensed matter physics. I like to develop Physics related apps and softwares from time to time. Can code in most of the popular languages. Like to share my knowledge in Physics and applications using this Blog and a YouTube channel.