Regarding the unit conversion of 1st q point

[muhammadhasan]

Hi,

I have a question regarding the LongDrXd. Following is my input parameters to find out dielectric function using IP-RPA. If you notice, I have used LongDrXd (1 | 0| 0) and run the simulation.

Code: Select all

optics                           # [R] Linear Response optical properties
chi                              # [R][CHI] Dyson equation for Chi.
dipoles                          # [R] Oscillator strenghts (or dipoles)
Chimod= "IP"                     # [X] IP/Hartree/ALDA/LRC/PF/BSfxc
% QpntsRXd
    1 |  721 |                       # [Xd] Transferred momenta
%
% BndsRnXd
   1 |  40 |                         # [Xd] Polarization function bands
%
% EnRngeXd
  0.00000 | 1.00000 |         eV    # [Xd] Energy range
%
% DmRngeXd
 0.003000 | 0.003000 |         eV    # [Xd] Damping range
%
ETStpsXd= 1000                    # [Xd] Total Energy steps
% LongDrXd
 1.000000 | 0.000000 | 0.000000 |        # [Xd] [cc] Electric Field
%

when I see my output results, I have seen it contains @ Q(1): 1.00000000 0.00000000 0.00000000 [q->0 direction], which is also OK.

# Absorption @ Q(1): 1.00000000 0.00000000 0.00000000 [q->0 direction]
#
# [ X ] Hartree size : 1
# [GEN] GF Energies : Perdew, Burke & Ernzerhof(X)+Perdew, Burke & Ernzerhof(C)
# [GEN] Green`s Function : T-ordered
#
# [GEN] Gauge : Length
# [GEN] [r,Vnl] included : yes
#
# E[1] [eV] Im(eps) Re(eps)

However, in the report file, the 1st q point is (as follows)
Q [ 1]: 0.000000 0.000000 0.000000 [rlu]
: weight : 0.123457E-3

IBZ Q-points : 721
BZ Q-points : 8100

K/Q-points units:
rlu = crystal or reduced units; cc = cartesian coordinates; iku = interal k-units

Q [ 1]: 0.000000 0.000000 0.000000 [rlu]
: weight : 0.123457E-3
Q [ 2]: 0.000000 0.011111 0.000000 [rlu]
: weight : 0.740743E-3
Q [ 3]: 0.000000 0.022222 0.000000 [rlu]
: weight : 0.740743E-3

even when I use ypp -grid q and then change the unit of q points from 'iku' to 'cc'. The 1st q point still same as 0 0 0. But it should be 1 0 0 .
Actually, for my research I need the dielectric function of each q point. So, when I use the simulation results in my research, should I change the 1st q point manually? For example: as in the report file, 1st q point is 0 0 0, would I have to change it to q 1 0 0 ? And then I will change the unit 'iku' to 'cc' with hand calculation (for 1st q point)?

Also, how about the weight? as the 0 0 0, weight : 0.123457E-3, the same weight will be applicable to 1 0 0?

Thank you so much.

Best
M J Hasan
PhD student
Mechanical Engineering
University of Maine

[Daniele Varsano]

Dear M J Hasan,

Let me clarify your doubts.

1) The first point of your grid is always (0,0,0) as reported in the report/output file.
2) The LongDrXd variable indicate the direction of the long wavelength limit (light absorption) that can differs depending on the direction if there is anisotropy. It essentially indicates the direction of the limit for q-->0.
3) If you want to calculate the response function for all q points, you need to specify them in QpntsRXd. In your input, I can see you have 721 points, and you should have the same number of outputs labelled by the q point index.

Hope now it is clear,

Best,
Daniele