# [Fortran] Is anyone familiar with the Elk-code software?

• Fortran
• Douasing
In summary, the conversation is about the Elk-code software and the difficulties the speaker is having while reading the source code. The speaker is specifically struggling with understanding the charge density and the calculation of the exchange-correlation energy density and potential. They are seeking clarification on the role of theta, phi, x, y, and z in these calculations. They ask for help and clarify that if their question is not clear, they are willing to provide more information.
Douasing
Dear all,

Are you familiar with the Elk-code software? It is a software about FLAPW (full potential linear augumented plane wave).Recently,I am reading the source code,but I meet many difficulties.

For example,I've a question related to charge density.In the Elk source code, the charge density is divided two parts,i.e.,rhomt(:,:,:) in the spherical coordinates and rhoir(:) in the Cartesian coordinates.But I don't find the angle (theta,phi) for the rhomt(:,:,:) and the position(x,y,z) for the rhoir(:) in the "rhomag.f90".
In addition,I want to learn about the calculating of the exchange-correlation energy density and potential,but I still can't find the (theta,phi) and (x,y,z),taking the xc_xalpha.f90 as an exmaple as follows:

! loop over density points
do i=1,n
r=rho(i)
if (r.gt.1.d-12) then
rs=(3.d0/(4.d0pir))(1.d0/3.d0)
rsm1=1.0d0/rs
! compute energy density
exc(i)=-alphaefacrsm1
! compute potential
vxc(i)=-alphavfacrsm1
end if
end do

Here,the "i=1,n" stands for the value of the radial meshgrid in the muffin-tin sphere and the value of G-point in the interstitial region.As my understanding,the energy density or potential should be for every point in the real space,so I don't clear why the (theta,phi) and (x,y,z) can't be found in those subroutines.

If anyone give me a hint or a suggestion,I will be thankful.
Regards,

By the way,if anyone will think my question is not clear enough, please say it to me,I will do my best to describe it.

## 1. What is Elk-code software?

Elk-code is a software package developed for electronic structure calculations of solids and molecules using the density functional theory (DFT) method.

## 2. What are the main features of Elk-code?

Elk-code offers a wide range of features such as self-consistent DFT calculations, non-self-consistent calculations for band structures, optimization of atomic positions, and calculation of magnetic properties.

## 3. Is Elk-code open source?

Yes, Elk-code is an open source software released under the GNU General Public License (GPL).

## 4. What programming language is Elk-code written in?

Elk-code is written in Fortran 90, with some parts in C and Python for post-processing and visualization.

## 5. Is Elk-code widely used in the scientific community?

Yes, Elk-code is a popular choice for electronic structure calculations and is used by researchers in various fields such as chemistry, physics, and materials science.

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