Page 1 of 1
A question about the variable "weight" in selfen_el.f90
Posted: Mon Aug 01, 2016 12:34 am
by Vahid
Dear EPW Users,
I have extracted the individual self-energy contributions from a 20x20x20 q grid to a list of k points for the diamond example case with no fsthick set. For a random k point (0,0.1,0.45), I considered the contributions that 3 equivalent q's make to the k point. The q points are
Code: Select all
0.0000000 0.0000000 0.0500000
0.0000000 0.0000000 0.9500000
0.0000000 0.0500000 0.0000000
Their six phonon energies are nearly the same
Code: Select all
8.478513578340556E-004 8.690353269845230E-004 1.371788110062204E-003
9.805869334826509E-003 9.807700191526363E-003 9.976014814358882E-003
8.478507370144750E-004 8.690347206693874E-004 1.371787569949127E-003
9.805869388560562E-003 9.807700244964069E-003 9.976014888855781E-003
6.409839467282880E-004 6.409839747712517E-004 1.300855935719668E-003
9.823412612494933E-003 9.823412614324758E-003 9.985488830814850E-003
But the weight variable calculated from
Code: Select all
weight = pi * wqf(iq) * ( (wgkq+wgq)*w0g1 + (one-wgkq+wgq)*w0g2 )
and their contributions to the k's self energy (2nd column) are quite different as shown below:
Code: Select all
2.840020921411006E-002 0.454447554214972
7.031015610841913E-004 0.163020527100226
4.599807289615457E-011 5.734701548147320E-010
Since the three q's have nearly the same energy while interacting with the same k electron, shouldn't the weights be the same?
Thank you,
Vahid
Vahid Askarpour
Department of Physics and Atmospheric Science
Dalhousie University,
Halifax, NS, Canada
Re: A question about the variable "weight" in selfen_el.f90
Posted: Wed Aug 03, 2016 10:40 pm
by Vahid
Hi,
I just would like to clarify that the weight I reported for the three q points were the last weights from the ik,imode,ibnd,jbnd loop. Otherwise, there are 96 weights in that loop for each ik and iq point which I did not report.
The self energies were calculated using the following matrix just before sigma_all's definition:
Code: Select all
sigmai_tot(ibnd,ik+lower_bnd-1,iq)=sigmai_tot(ibnd,ik+lower_bnd-1,iq)+g2*weight
So the three self energies contributed by the three q's were summed over the bands and modes.
Cheers,
Vahid
Re: A question about the variable "weight" in selfen_el.f90
Posted: Thu Aug 04, 2016 10:47 am
by sponce
Hello Vahid,
You should check that the sum of the 96 weight is correctly 1 (or eventually 2).
If the point are truly random, the weight is likely to be 1.0/96 indeed.
Best,
Samuel
Re: A question about the variable "weight" in selfen_el.f90
Posted: Fri Aug 05, 2016 12:17 am
by Vahid
Hello Samuel,
Thank you for suggesting to check the sum of the weights. For the first q point and the k point I reported in my first post, I get these 96 weights which come from the 6 modes and 4 bands:
Code: Select all
7.762864806541902E-004 1.900714716071483E-088 1.900714716071483E-088
1.900714716071483E-088 1.900714716071483E-088 1.021064846680064E-004
1.900714716071483E-088 1.900714716071483E-088 1.900714716071483E-088
1.900714716071483E-088 3.449724804790480E-003 3.624470068423790E-015
1.900714716071483E-088 1.900714716071483E-088 1.392555733007761E-013
1.162868088328380E-002 7.658697008806053E-004 1.855903177856707E-088
1.855903177856707E-088 1.855903177856707E-088 1.855903177856707E-088
9.988768852914349E-005 1.855903177856707E-088 1.855903177856707E-088
1.855903177856707E-088 1.855903177856707E-088 3.365972178129029E-003
3.608760629646159E-015 1.855903177856707E-088 1.855903177856707E-088
1.402167782315355E-013 1.142397687925616E-002 6.597723509642105E-004
1.205415093427186E-088 1.205415093427186E-088 1.205415093427186E-088
1.205415093427186E-088 6.851838511100885E-005 1.205415093427186E-088
1.205415093427186E-088 1.205415093427186E-088 1.205415093427186E-088
2.138126564063455E-003 3.884992399302110E-015 1.205415093427186E-088
1.205415093427186E-088 1.951103389053494E-013 8.807905983448494E-003
1.137642909376745E-002 4.219810241638788E-089 4.219810241638788E-089
4.219810241638788E-089 4.219810241638788E-089 2.757438543751118E-005
4.219810241638788E-089 4.219810241638788E-089 4.219810241638788E-089
4.219810241638788E-089 1.248181676748954E-004 1.651540243905585E-012
4.219810241638788E-089 4.219810241638788E-089 3.572659187442366E-009
2.806613303790095E-002 1.138197790051863E-002 4.219763605397296E-089
4.219763605397296E-089 4.219763605397296E-089 4.219763605397296E-089
2.756630180454055E-005 4.219763605397296E-089 4.219763605397296E-089
4.219763605397296E-089 4.219763605397296E-089 1.247326477863427E-004
1.653477104954179E-012 4.219763605397296E-089 4.219763605397296E-089
3.579755515211524E-009 2.806986024830347E-002 1.189778235600534E-002
4.215664645084622E-089 4.215664645084622E-089 4.215664645084622E-089
4.215664645084622E-089 2.681959948975107E-005 4.215664645084622E-089
4.215664645084622E-089 4.215664645084622E-089 4.215664645084622E-089
1.170590554948513E-004 1.840659337997957E-012 4.215664645084622E-089
4.215664645084622E-089 4.293959613693773E-009 2.840020921411006E-002
0.454447554214972
They do not add up to 1 or 2. 0.4544 is the largest with the sum just over 0.56.
I obtained these weights by defining a new matrix wght as follows right after the definition of weight in my first post:
Code: Select all
wght(ibnd,jbnd,imode,ik+lower_bnd-1,iq)=weight
The q points are not random. The fine q grid is 20x20x20.
So now there are two issues:
1. the weights do not add up to either 1 or 2.
2. I was expecting the three (symmetrically equivalent) phonons to make almost equal contributions to the self-energy of the k point but they are vastly different as I reported in my first post. May be this is due to incorrect weight values.
Best,
Vahid
Re: A question about the variable "weight" in selfen_el.f90
Posted: Mon Aug 08, 2016 10:42 am
by carla.verdi
Dear Vahid
I think there was some slight confusion about the weights - they do not need to add up to 1 or 2 as they are the self-energy factors without the matrix element.
I understand that the q points you considered are equivalent, but I suppose the k+q points are not, so the eigenenergies at k+q will not be the same (hence the 'weight' quantity will be different).
Best
Carla
Re: A question about the variable "weight" in selfen_el.f90
Posted: Mon Aug 08, 2016 4:41 pm
by Vahid
Dear Carla,
Thank you for the clarification. I was under the impression that symmetrically equivalent q phonons will interact with a k electron and result in symmetrically equivalent k+q states which naturally have identical energies based on energy conservation. I guess I was wrong.
Best wishes,
Vahid