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Dear Valerie,
the output to EVALSV*.OUT is hard-coded, and you cannot avoid it just by adding some options to an input file. What is the reason why you would like to skip the output to these files?

Dear Dr. Cocchi

Thank you very much. I got it.

Best wishes

M. Tarighi
Malek-Ashtar university of technology
Iran

Dear Mahdi Tarighi,

the RPA spectrum includes the bare Coulomb interaction, which is given by the exchange term in the BSE Hamiltonian. This term blue-shifts the absorption onset compared to the independent-particle approximation, where only vertical transitions are accounted for. The size of this effect depends on the material.

By comparing the BSE result with the RPA spectrum one gets the binding energy due only to the electron-hole attraction but the exchange interaction is not accounted for.

Best regards,
Caterina Cocchi
(exciting team)

Dear Dr. Cocchi

Thanks for your illustrative comment. But, according to the BSE hamiltonian, the difference between singlet and RPA modes is just direct term, which is nothing but electron-hole interaction. So, are you sure that when we are calculating exciton binding energies we have to look at lowest-energy independent-particle transition rather than RPA one?

Best

M. Tarighi
Malek-Ashtar university of technology
Iran

Dear exciting-team,

is there an input option to avoid the temporary write-out of the program to EVALSV#-#.OUT etc. files?

Thank you,
Valerie

Avoid file I/O to temporary files by Valerie (guest), 21 Apr 2017 13:47

Dear Mahdi Tarighi,

the convention that we use in exciting to evaluate exciton binding energies is the following. Exciton binding energies, printed in the third column of the BSE output files EXCITON_BSEsinglet_XXX.OUT, are obtained as the difference between the excitation energies (second column) and the lowest-energy independent-particle transition. The energy of the latter corresponds to the optical gap of the system. Slight differences between this quantity and the optical gap printed in the output of a GW calculation may be ascribed to different k-meshes adopted in either calculation.

Although many definitions of the exciton binding energy appear in the literature, in general I would not recommend to evaluate it with respect to the fundamental gap (which may be indirect) but rather to the optical gap.

I hope this solves your doubts.

Best regards,
Caterina Cocchi
(exciting team)

As we know, exciton binding energies are energy difference between fundamental (or quasiparticle corrected) gap and excitation energies of bound excitonic states. But we see in the tutorial "Excited States from BSE" that we must consider the gap appeared at the end of file "EXCITON_BSEsinglet_***.OUT" which is far away from fundamental gap and is very close to the optical gap (which is printed in the output of G0W0 calculation). Then, my question is that why we don't get confused with the right gap?

Best regards

M. Tarighi
Malek-Ashtar university of technology
Iran

Dear Hajar,

sure, LayerOptics can still be an useful tool also in your case. For instance, you may use it to simulate a specific orientation of your material with respect to the light beam.

Feel free to contact us again for any further question related to it.

Best wishes,
Caterina Cocchi
(exciting team)

by Caterina CocchiCaterina Cocchi, 19 Apr 2017 07:29
Hajar (guest) 18 Apr 2017 16:42
in discussion Forum / Support Questions » layeroptics for the bulk materials

Dear Caterina
Thank you very much for your complete response. This is so valuable.

My cases are orthorhombic, hexagonal and tetragonal, NOT monoclinic or triclinic ("epsilon_xx=epsilon_yy," and "epsilon_xy=epsilon_xz=epsilon_yz=0").
Since my cases are anisotropic, is Layeroptics helpful for my cases?!!

Thanks for your attention

Hajar

by Hajar (guest), 18 Apr 2017 16:42

Dear Hajar,

LayerOptics is meant to calculate optical coefficients starting from dielectric tensors computed for bulk materials regardless of their atomic morphology. This tool is particularly useful in case of anisotropic systems in which the off-diagonal elements of the tensor are non-negligible. Is this the case of your material? Is it a monoclinic or triclinic lattice?

To answer your specific questions, you have to bare in mind that LayerOptics always assumes the presence of a substrate, whose dielectric function is hard-coded (in the current distribution we inserted bulk silicon, but this value can be changed by the user), and a vacuum layer on top. So if you are going to input only one computed dielectric tensor, you will need to insert "1" when you are asked to provide the number of layers. Concerning the thickness, the idea is to simulate interfaces at the nanoscale. This could be the case of a molecular crystals, which are usually grown in samples with a certain thickness. In general this value does not impact much the final result, except for absolute value of the optical coefficients. We recommend the user to choose values around 10 nm.

I hope these indications will help you solving your problem.

Best regards,
Caterina Cocchi
(exciting team)

Dear exciting-code developers
I want to calculate optical coefficients for a bulk material (not a layer) containing some stacking layers along the c axis, by the layeroptics software.
Since my case has not a vacuum, what is the response of these two steps: 1. 'Provide the number of layers'? 2. For each layer. specify the thickness (nm).

my case has 10 layers in its unit cell along the c dimension.
Thanks a lot

layeroptics for the bulk materials by Hajar (guest), 07 Apr 2017 13:20

Dear Caterina,
Thanks very much to your great team for developing this code. We are looking for the next release.

Best

Dear iceaiai,

there is no fixed date planned for next release yet, but we expect to deliver one this year.

Best regards,
Caterina Cocchi
(exciting team)

Dear Caterina,
Thanks very much for your explanation. I saw a great improvement in the spin-orbital splitting in the carbon version. Looking forward to the next version. Is there an estimated time for the next release?

Dear iceaiai,

the calculation of core excitations in presence of partially occupied states is currently under development and will be included in the next release of exciting.

Best regards,
Caterina Cocchi
(exciting team)

Dear Caterina,
I really appreciate for your answers. I will do some dos first to improve the model.
I have a question to ask. Is it possible to calculate graphene XAS using BSE by setting K-S gap to zero or changing the smearing? We have an unusual EELS of boron in graphene in a paper. Hopefully we can use exciting-code to solve this problem.

iceaiai (guest) 29 Mar 2017 14:24
in discussion Forum / Support Questions » Warning(xas_scrcoulint): There is no KS-gap present

Dear Caterina,
I really appreciate for your answers. I will do some dos first to improve the model.
I have a question to ask. Is it possible to calculate graphene XAS using BSE by setting K-S gap to zero or changing the smearing? We have an unusual EELS of boron in graphene in a paper. Hopefully we can use exciting-code to solve this problem.

by iceaiai (guest), 29 Mar 2017 14:24

Dear iceaiai,

this message is appearing because the system under study has partially occupied states. This is not a very unusual scenario in case of doped materials like yours. There is nothing wrong with the exciting code. I suggest you to improve your ground-state parameters and check whether your system indeed has a gap or not.

Best regards,
Caterina Cocchi
(exciting team)

Dear developer,
When I calculate B doped diamond, I encountered the following error:
There is no KS-gap present

It is strange cause the diamond is insulator.

I attached my input file as following. Thanks to read my post.
<?xml version="1.0"?>

-<input>

<title>B in Graphite</title>

-<structure speciespath=".">

-<crystal scale="1.88973">

<basevect>3.5559999943 0.0000000000 0.0000000000</basevect>

<basevect>0.0000000000 3.5559999943 0.0000000000</basevect>

<basevect>0.0000000000 0.0000000000 3.5559999943 </basevect>

</crystal>

-<species rmt="1.25" speciesfile="C.xml">

<atom coord="0.00000000 0.00000000 0.00000000"/>

<atom coord="0.00000000 0.50000000 0.50000000"/>

<atom coord="0.50000000 0.00000000 0.50000000"/>

<atom coord="0.75000000 0.25000000 0.75000000"/>

<atom coord="0.25000000 0.25000000 0.25000000"/>

<atom coord="0.25000000 0.75000000 0.75000000"/>

<atom coord="0.75000000 0.75000000 0.25000000"/>

</species>

-<species rmt="1.25" speciesfile="B.xml">

<atom coord="0.50000000 0.50000000 0.00000000"/>

</species>

</structure>

<groundstate xctype="GGA_PBE_SOL" gmaxvr="20" ngridk="4 4 4" rgkmax="6.0"> </groundstate>

-<xs ngridk="4 4 4" rgkmax="6.0" tevout="true" broad="0.018" gqmax="3.0" nempty="50" vkloff="0.05 0.15 0.25" ngridq="4 4 4" xstype="BSE">

<energywindow points="1500" intv="3.0 7.0"/>

<screening nempty="100" screentype="full"/>

<BSE nstlxas="1 15" bsetype="singlet" xasedge="K" xasatom="1" xasspecies="2" xas="true"/>

-<qpointset>

<qpoint>0.0 0.0 0.0</qpoint>

</qpointset>

</xs>

</input>

Warning(xas_scrcoulint): There is no KS-gap present by iceaiai (guest), 28 Mar 2017 19:31
vkloff
koppolu mahendrakoppolu mahendra 22 Mar 2017 08:38
in discussion Forum / Controversy » vkloff

If any one of the experts of the TDDF explains about "vkloff", can be very helpful for beginners like me.

vkloff by koppolu mahendrakoppolu mahendra, 22 Mar 2017 08:38
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