Input file generation

In this module you will learn how to generate and modify an input file with Yambo.

Prerequisites

Previous modules

• Initialization for bulk hBN or 2D hBN

Below you will find all the instructions for the bulk hBN case.

You will need:

• The SAVE databases for bulk hBN
• The yambo executable

Input file generator

First, move to the appropriate folder and initialize the Yambo databases if you haven't already done so.

$ cd YAMBO_TUTORIALS/hBN/YAMBO
$ yambo        

Yambo generates its own input files: you just tell the code what you want to calculate by launching Yambo along with one or more lowercase options. (Uppercase options are considered in the following section).

To see the list of runlevels and options, run yambo -h or better,

$ yambo -H
Tool: yambo 4.1.2 rev.14024
Description: A shiny pot of fun and happiness [C.D.Hogan] 
[Upper case options]
-i		:Initialization
-o <opt>	:Optics [opt=(c)hi is (G)-space / (b)se is (eh)-space ]
-k <opt>	:Kernel [opt=hartree/alda/lrc/hf/sex] 
-y <opt>	:BSE solver [opt=h/d/(p/f)i]  
                (h)aydock/(d)iagonalization/(i)nversion
-r		:Coulomb potential
-x		:Hartree-Fock Self-energy and local XC
-d		:Dynamical Inverse Dielectric Matrix
-b		:Static Inverse Dielectric Matrix
-p <opt>	:GW approximations [opt=(p)PA/(c)HOSEX]
-g <opt>	:Dyson Equation solver
                [opt=(n)ewton/(s)ecant/(g)reen]
-l		:GoWo Quasiparticle lifetimes
-a		:ACFDT Total Energy

Any time you launch Yambo with a lowercase option, Yambo will generate the appropriate input file (default name: yambo.in) and launch the vi editor.

Editor choice can be changed at configure; alternatively you can use the -Q run time option to skip the automatic editing (do this if you are not familiar with vi!):

$ yambo -x -Q
yambo: input file yambo.in created
$ emacs yambo.in     or your favourite editing tool

Combining options

Multiple options can be used together to activate various tasks or runlevels (in some cases this is actually a necessity). For instance, to generate an input file for optical spectra including local field effects (Hartree approximation), do (and then exit)

$ yambo -o c -k hartree       which switches on:
optics                       # [R OPT] Optics
chi                          # [R CHI] Dyson equation for Chi.
Chimod= "Hartree"            # [X] IP/Hartree/ALDA/LRC/BSfxc

To perform a Hartree-Fock and GW calculation using a plasmon-pole approximation, do (and then exit):

$ yambo -x -g n -p p        which switches on:
HF_and_locXC                 # [R XX] Hartree-Fock Self-energy and Vxc
gw0                          # [R GW] GoWo Quasiparticle energy levels
ppa                          # [R Xp] Plasmon Pole Approximation
em1d                         # [R Xd] Dynamical Inverse Dielectric Matrix      

Each runlevel activates its own list of variables and flags.

Changing input parameters

Yambo reads various parameters from existing database files and/or input files and uses them to suggest values or ranges. Let's illustrate this by generating the input file for a Hartree-Fock calculation.

$ yambo -x

Inside the generated input file you should find:

EXXRLvcs =  3187        RL    # [XX] Exchange RL components
%QPkrange                    # [GW] QP generalized Kpoint/Band indices
  1| 14|  1|100|
%

The QPkrange variable (follow the link for a detailed explanation) suggests a range of k-points (1 to 14) and bands (1 to 100) based on what it finds in the core database SAVE/ns.db1, i.e. as defined by the DFT code. Leave that variable alone, and instead modify the previous variable to EXXRLvcs= 1000 RL

Save the file, and now generate the input a second time with yambo -x. You will see:

 EXXRLvcs=  1009        RL

This indicates that Yambo has read the new input value (1000 G-vectors), checked the database of G-vector shells (SAVE/ndb.gops), and changed the input value to one that fits a completely closed shell.

Last, note that Yambo variables can be expressed in different units. In this case, RL can be replaced by an energy unit like Ry, eV, Ha, etc. Energy units are generally better as they are independent of the cell size. Technical information is available on the Variables page.

The input file generator of Yambo is thus an intelligent parser, which interacts with the user and the existing databases. For this reason we recommend that you always use Yambo to generate the input files, rather than making them yourself.

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