# First-principles Calculations

How to find the Band structure of a material using VASP?
I would like to find the band structure and I have to give the Brillouin Zone path, But How? Please suggest me any video lectures or PDF for this content.
Danilo Puggioni · Drexel University
To generated ``strings'' of k-points connecting specific points of the Brillouin zone, the third line of the KPOINTS file must start with an ``L'' for line-mode: k-points along high symmetry lines 10 ! 10 intersections Line-mode cart 0 0 0 ! gamma 0 0 1 ! X 0 0 1 ! X 0.5 0 1 ! W 0.5 0 1 ! W 0 0 1 ! gamma VASP will generate 10 k-points, between the first and the second supplied point, 10 k-points between the third and the fourth, and another 10 points between the final two points. The coordinates of the k-points can be supplied in cartesian (4th line starts with c or k) or in reciprocal coordinates (4th line starts with r): k-points along high symmetry lines 10 ! 10 intersections Line-mode rec 0 0 0 ! gamma 0.5 0.5 0 ! X 0.5 0.5 0 ! X 0.5 0.75 0.25 ! W 0.5 0.75 0.25 ! W 0 0 0 ! gamma
• Peram sreenivasa Reddy asked a question:
How do you install KKR-ASA code and how do you run the examples?
I want to install the KKR-ASA code in my system. In the code folder I have subfolders named bgfm, blas, bstr, lmtolib, lsgf, and spcm. I went into the folder bgfm/source and put make option in my terminal. Finally it is showing that the file named lmtolib is not there. How can I prevent this from happening? Can someone show me an example?
What is CPA-EMTO code?
I want to know about the CPA-EMTO code. Where can I get this code for a sample test?
Krisztián Palotás · Budapest University of Technology and Economics
Probably the best is to contact Prof. Levente Vitos directly, he could provide you details with the CPA-EMTO code. Good luck!
Is UFF (Universal Force Field) potential a good choice for modelling metal clusters?
I tried both UFF and EAM for such systems and EAM potentials seems to be producing better results.
thanks for your reply. i tried up to 30 atom clusters for Pd with UFF and EAM. But UFF (with gulp, and i used a genetic algorithm to search for global minima) is not giving very much coherent results, whereas with EAM I am getting .regular shaped clusters.
How to confirm that my band gap is correct in the absence of experimental results?
I calculated band gap for my material and I want to confirm with experimental results but I seem to have encountered an absence of experimental results. What's another way?
Marcin Andrzejak · Jagiellonian University
Find a functional that is most commonly used in such problems and based on the published results for systems, for which experimental data exist, determine the errorm margin. This can give you some estimate where energetically your band-gap may lie. Otherwise, find a suitable research group and try to convince them to measure the band gap for your material. This is probably the safest way...
How create a crystal structure in Material studio for AB0.5C0.5O3?
A-0 0 0 B 0.5 0.5 0.5 C 0.5 0.5 0.5 O 0.5 0.0 0.5 O 0.5 0.5 0.0 O 0.. 0.5 0.5
to make a crystal structure, three parameters are needed: shape (space group), size (lattice parameter) and location of atoms (fractional coordinates). if you have all of these, then make a 3D atomistic document---->Build-crystals-Build Crystal--->input lattice parameters and space group to make the empty cell. Then you can insert atoms in the structure from Build-Add Atoms. (P.S. assuming the data you have mentioned above are fractional coordinates, there is one severe inconsistency - Both B and C are situated at the same location. From these I get the picture that 6 O atoms at the face centres, 1/8th of A as it is sitting in a corner and 1 each of B and C as they are sitting in middle of the cell!)
• Zuheir El-bayyari asked a question:
The Role of Pd-Re Alloys in Medical Devices and its applications? In what shape and structure?
I want to understand and simulate such alloys to study their structural stability with increasing temperature. Any comments please?
Is it possible to predict electronic transition properties of a molecule based on its molecular orbitas?
I have an organic structure. I want to predict and judge its transition properties. Could I judge about it based on its LUMO? How can I predict about its transition properties based on molecule's ground state?
Thank you very much for your attention. As you know every molecule has energy Gap. And, I have HOMO- Highest Occupied Molecular Orbital- energy; and, also LUMO- Lowest Unoccupied Molecular Orbital. Then, imagine we have attached the molecule to the leads. Now, electron flow will pass through the cluster. Could I tell that this additional electron, injected from the source, will occupy HUMO? Means that by passing the current through the molecule, additional electron will occupy LUMO state?
How to understand the reciprocal space (k-space). How will it work in PwScf calculation?
I am very confusing about reciprocal space. It does not exist but why we are using and what is the role of k-points in PwScf calculations.
Roman Leitsmann · AQcomputare Company
In quantum mechanics the wave functions |psi> can be represented in different ways. One way the the real space representation of the wave function psi(r) = <r|psi>, another possibility is the k-space representation psi(k) = <k|psi>. Both representations are conneted via a Fourier-transfomation. In this sense both representations exist.
What software to use for Raman and IR theoretical modes?
Is there any free software to find Raman theoretical modes? I know Gaussian 3 package but it is a licensed version.
Sanjiv Jha · New Mexico State University
PWSCF (Quantum Espresso) can be used to study the Raman (the system should not be a metallic one) and IR spectra of the system. Also, the software is free.
How to explain Raman (also IR) active or inactive modes?
In point group table I observed the modes. Some are Raman active and some are IR active? How should we explain those modes? Let's we take one example: Point group D2h(mmm).
Gyorgy Banhegyi · Bay Zoltán Nonprofit Ltd. for Applied Research
Hugh, it was long time ago. Anyway: IR activity presupposes non-zero transition dipole moment, while Raman activity presupposes non-zero transition polarizability. Those modes which transform similarly to x, y or z (as shown by the character table) are IR active, while those, which transform similarly to xy, yz or xz are Raman active. See e.g. http://books.google.hu/books/about/Molecular_Vibrations.html?id=CPkvsDrPiv0C&redir_esc=y
How the "smearing" will affect the geometry optimization and density of states (DOS) when calculated by the Density Functional Theory?
During electronic structure calculations and geometry optimization using DFT, smearing is used which replaces smooth functions in place of actual functions of DOS. What is the drawback in using this smearing? Using large smearing values causes structural deformations. Why?
smearing excites electrons into the virtual space. This has the effect of smoothing SCF convergence, but it also increases the anti-bonding character of the wavefunction. As you go to higher smearing you push more electrons into the virtual space and destabilize the system. Eventually, your smearing will make the system totally unphysical. The advantage of the method is that it improves SCF converge a LOT in many cases. I think the maximum value that you choose is a judgment call. When I need smearing, I start at 0.005 au. I will not go over 0.010 au. If I need larger smearing then there is usually something wrong, like bad geometry or wrong spin state. Most DFT programs will print both the total energy with smearing and extrapolated to zero smearing. If those values are getting too far apart then you know your smearing is too large
• Kebbab Zoubir asked a question:
Is there free software (like phonon code) which can help us for studying phonon dispersion in solid materials?
Any free software which can be used with DFT calculation (like Win2k code)?
How to find Cartesian atomic coordinates of Silicon in a unit cell on a surface?
How can one find these or reciprocal coordinates for a couple of layers in a slab?
Andrii Vasylenko · National Academy of Sciences of Ukraine
It clarifies a lot =) Thank you for such a helpful answer, Deniel. References on software are really valuable. P.S. Why I thought of such a small amount of atoms for a surface case... it was a mistaken suggestion only, which goes out of a correct way of calculating the bulk Silicon with 2 atoms per unit cell though. 0.0 0.0 0.0 1/4 1/4 1/4 That gave me a feeling that one might add an atom on top of it to get a "slab" unit cell in 111 direction
How to properly apply Gaussian G2 method?
I would like to ask what is the proper way to use this Gaussian composite method for high-accurate energy calculations? Do I need to pre-optimize my molecule using the same functional and basis set (in this case: MP2/6-31G*) as its required for starting geometry in G2 method? Or maybe this pre-optimization step is done automatically within G2 method and there is no difference what functional/basis set was used to prepare initial structure? Moreover, should I use OPT keyword or just G2 alone? I noticed that in case of correcting energies of transition state structures, the OPT(TS) keyword was needed, otherwise the molecule was optimized either to reactants or products.
José Gomes · University of Aveiro
Q: "Or maybe this pre-optimization step is done automatically within G2 method..." A: Yes, if you use G2 keyword the geometry will be optimized at the HF/6-31G(d) level of theory (first step). Then (2nd step), frequencies will be calculated at the same level of theory. In the 3rd step, the structure will be further optimized at the MP2(Full)/6-31G(d) level. The geometry optimized in the latter step will be used for single-point calculations at the QCISD(T,E4T)/6-311G(d,p), 4th step, MP4/6-311+G(d,p), 5th step, MP4/6-311G(2df,p), 6th step, and MP2/6-311+G(3df,2p), 7th step, levels of theory. Q: "there is no difference what functional/basis set was used to prepare initial structure?" A: G2 will optimize the structure provided in the input file (initial structure) to the closest minimum on the potential energy surface (i.e., it will be optimized at the HF/6-31G(d) level of theory and then, steps 2-7 above will follow in cascade).
How do you identify the energy levels of a1, a2 and e states from Density of States Plot?
We know that due to C3v symmetry, energy levels splits into a1, a2, and e states. How do you identify the approximate energy level of each state (a1, a2 and e1) from Density of states of a particular system?
Roshanak Teymoori · University of Alberta
hi this is the same question I have !!! I am doing gaussian calculation for VOF3 and would like to know how to assign each energy levels based on a1, a2, e?
How to calculate the enthalpy of formation using the first principle calculation result?
For example I have the total energy of the following: Mg2Ni (hcp): a eV, Mg (hcp): b eV, Ni (fcc): c eV. In the cell of Mg2Ni, Mg and Ni there are 36, 2, 14 atoms, but considering not all atoms contribute solely to one cell, the real numbers of atoms in a cell are Mg12Ni6, Mg2, Ni4, so: Enthalpy of formation of Mg2Ni: a/6-b-c/4 However I found this doesn't agree with what I've found in other's articles.
Xianda Li · Institut Franche-Comté Electronique Mécanique Thermique et Optique Sciences et Technologies
Well I think I've found the problem. It's due to the wrong Ni numbers in a fcc nickel cell. When it was calculated, it has used the primitive cell which has only 1 nickel atom in the cell rather than the conventional cell. So the correct way should be: a/6-b-c
How to set up GW+BSE calculation in VASP?
I am trying to set up GW/BSE calculation on VASP (new version 5.3), Does anyone have an idea about it ? Please share your view !
Mukesh Kumar · National Institute for Materials Science
Thank you for reply ! I will check Abinit...
What are good references for learning the necessary programming for first principles calculations of material properties?
Also, what are good references for the approach of first principles calculations, i.e. how crystal structure affects properties, how nearest neighbor interactions affect the properties, etc.?
Dinesh Dixit · Indian Institute of Technology Bombay
@Jeffrey Sir......thank you so much.
How to perform IRCMax(CBS-QB3:B3LYP/6-311G(d,p)) calculations in Gaussian?
I have been recently trying to perform IRCMax calculation to follow minimum energy path MEP obtained at B3LYP/6-311G(d,p) level of theory in order to find a maximum energy along this path using CBS-QB3 method. However, I couldn't even run my simulations due to syntax error. Does anyone know what is the proper way to perform this calculation? I was using the following expression in my route section in Gaussian: #p IRCmax(CBS-QB3:B3LYP/6-311G(d,p),Zero)
Thanh Nguyen · University of Texas at Austin
Dear Daniel: I faced this problem six years ago because I wanted to get IRCMax(CBS-QB3) for WKB approach. As far as I know, we cannot run this calculation automatically using Gaussian. Have you asked Gaussian's people this question? I have not. For my case, I have to run this calculation manually, first run IRC with B3LYP, and then run single-point energy calculation with CBS-QB3. For each geometry along the reaction path, you can run a single point energy calculation with CBS-QB3 as below: 1) #B3LYP 6-311G** freq .. .. .. 2) #CBS-QB3(StartMP2) geom=check guess=read Do not hesitate to contact me: lnguyen@cm.utexas.edu Lam
Is there any reference or an artcile that explains surface magnetism interms of energy level diagrams?
Any reference on "How the energy levels split due to surface magnetism?"
Sandhya ch · National University of Singapore
Thank you Dr. Kai Fauth.
How to design and calculate the energy cut-off three layer structure? B layer occupied interstitute between A layer and C layer.
Some atoms of A structure and an atom of B structure vacancy were interstituted by B structure, how should I determine the energy cut-off and K point (or others)?
Hassakorn Wattanasarn · Sakon Nakhon Rajabhat University
If lattice constant a , b, c about 3.9, 5.3, 15.2 respectively, the k point and energy cut off should be large or small. Moreover, I found that either band gab very very low or not show value which the elements does not metal.
• Jinping Li asked a question:
Why does band gap firstly increase, and then drop, there is a max. with the rise of Ud?
When I calculate electronical structure and optical properties of m-HfO2, c-HfO2 and c-ZrO2 by use of LDA+Ud+Up or GGA+Ud+Up methods, the band gap firstly increases, and then decreases, there is a max. with the rise of Ud for Hf 5d or Zr 4d orbital. While, the band gap increases gradually with the rise of Up for O 2p orbital. Who can give me the reason?
Can you tell me the difference between LDA, B3LYP, sX, sX-LDA and LSDA+U?
When I calculate electrical structure and optical properties of cubic-HfO2 or cubic-ZrO2 by first principles method, I can not explain the different calculation results from different methods, such as LDA, B3LYP, sX, sX-LDA and LSDA+U. Can you tell me the reason?
Jordi Toda · University of Aveiro
First of all you may notice that you are working with functionals that belong to diffrent families: LDA is local, B3LYP is hybrid, sX-LDA is non-local, and LSDA+U is a DFT+U type where you are introducing an external correction to the energy. It is normal that you have such differences because you are not working with the same methods. (even PBE and PW91 that are both of the GGA family provides diffrent results). Notice that LDA energy only depends on the value of electronic density at each point on the space. On the other hand, in the hybrids functionals the exact exchange energy functional is expressed in terms of the Kohn-Sham orbitals rather than the density. Furthermore, the LDA+U method was developed to improve the band gaps provided by the pure LDA, and the sX-LDA is in the same way. You can use your results to show the different accuracy of your methods and choose the best one.
Can VASP realize first-principles molecules dynamics simulation?
I want to simulate oxide and absorbtion on the surface of ceramic composites under ultrahigh temperature. Can VASP realize first-principles molecules dynamics simulation? Can you tell me which softpackage is best for ultrahigh temperature ceramics? Why?
Jinping Li · Harbin Institute of Technology
Thank Dear Sayede for your answering my question. Your saying is right, and VASP can do so really. I will learn how to use VASP. Thank you very much.
How to decide U value when we calculate materials properties by first-principles GGA+U method?
I think Ud=8.25eV for Hf atoms is better when I calculate cubic-HfO2 by GGA+U method, while Ud=8.25ev for Zr atoms is not too good when I calculate cubic-ZrO2 by GGA+U method. How much about Ud for Zr atoms is good? When I calculate Zr0.667Hf0.333O2 solid solutions by GGA+U, how much abour Ud for Hf atoms and Zr atoms are? We know band gap of HfO2 is 5.7eV, of ZrO2 is 5.5eV, How much is band gap of Zr0.667Hf0.333O2 solid solutions? There is a paper to report that it is 5.3eV, I think it maybe is in middle of 5.7-5.8eV, why does it become small?
Jinping Li · Harbin Institute of Technology
Thank dear Toda for his answering my question. I think that U value is not an empirical parameter and it can be obtained by strictly exporting from physics theory. Of course, it is most possible to cost much time and need profound physical knowwledge. Without these, like me, only by hand can I get better results by use of LSDA+U methods.