Response for large Q vector

[feffeficus]

Hi again.

I would like to calculate the response function (alda /rpa) for large Q vector (transferred momenta), such as Q = q + G, where q is a q vector of the IBZ, to study in particular eels spectra.

Since what I understand in Yambo the way to specify the q vector is with:

% QpntsRXd
1 | 216 | # [Xd] Transferred momenta

so specifying the index of the q vector from the list we have in the r_setup file after the initialization.
but to me the q vector we have in this list belong all to the IBZ.

Zoooo, my questions:

1) how can I specify a q vector in yambo.in by giving explicitly the coordinates (relative lattice units? cartesian?) Which flag?
2) how can I then specify to yambo a bigger Q vector? For example that belongs to a larger Brillouin zone??

Please tell me and correct me when I'm wrong.

Thanks again so much!
federico iori.

[andrea marini]

1) how can I specify a q vector in yambo.in by giving explicitly the coordinates (relative lattice units? cartesian?) Which flag?
2) how can I then specify to yambo a bigger Q vector? For example that belongs to a larger Brillouin zone??

Dear Federico,

at the moment it is not possible to pick up a Q vector outside the IBZ. However this feature was possible in an old version of the code. It was removed because not used so often. Let me see if I can find it (it should be somewhere on the repository). I will let you know.

[feffeficus]

grazie Andrea!

I know it's a little bit unsual maybe since the calculation are heavy, but here to study this orrible V_$2$O_$3$ we are obliged to go higher with the q vector to focus on the d states and d-d transitions also.

thanks so much!

PS: i will give a look at the a2y stuff also!

[andrea marini]

Large Q calculations has been added to the latest revision in the SVN repository. Check here for more informations.

To use this feature increase the verbosity by using

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>yambo -o c -V resp

Then use the two variables

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Qdirectionn
QShiftOrder

to specify the direction along which you want the q+G vector ro lay and to choose among all vectors that lay in that direction the (QShiftOrder)th. Moreover use all possible Q-vectors because of the two above fields are present Yambo will only calculate the q+G combinations that lay in the wanted direction. For example the input file of a system with 48 Q-points in total that calculates the eps/eels along the z direction and picks-up the second q+G is

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% Qdirection
 0.000    | 0.000    | 1.000    |      # [Xd] Transferred momentum direction (iku)
%
QShiftOrder= 2               # [Xd] Pick-up the (QShiftOrder)th q+G vector
% QpntsRXd
   1 |  48 |                 # [Xd] Transferred momenta
%