Exciton-phonon coupling and luminescence - Revision history

FulvioPaleari: /* Step 6: obtain the electron-phonon matrix elements */

2026-03-13T14:56:00Z

Step 6: obtain the electron-phonon matrix elements

← Older revision		Revision as of 14:56, 13 March 2026
Line 294:		Line 294:
	you will see that yambopy has created the Yambo-compatible electron-phonon databases.		you will see that yambopy has created the Yambo-compatible electron-phonon databases.

	If you want to run LetzElPhC directly, without using yambopy, you can refer to its [[https://~~gitlab~~.com/~~lumen~~-code/LetzElPhC/-/blob/main/docs/main.pdf~~?ref_type=heads~~\|user guide]].		If you want to run LetzElPhC directly, without using yambopy, you can refer to its [https://github.com/yambo-code/LetzElPhC/blob/main/docs/tex_doc/main.pdf\|user guide].
	Keep in mind that in this case, in order to convert the database to the <code>ndb.elph_gkkp*</code> databases of Yambo, you will then need a couple of lines of python using the Yambopy class <code>ConvertElectronPhononDB</code> in <code>yambopy/letzelph_interface/lelph2y.py</code>.		Keep in mind that in this case, in order to convert the database to the <code>ndb.elph_gkkp*</code> databases of Yambo, you will then need a couple of lines of python using the Yambopy class <code>ConvertElectronPhononDB</code> in <code>yambopy/letzelph_interface/lelph2y.py</code>.

FulvioPaleari at 14:47, 13 March 2026

2026-03-13T14:47:46Z

← Older revision		Revision as of 14:47, 13 March 2026
Line 1:		Line 1:
	[[~~exc-ph scheme\|~~ Tdgw-phonon-usc-01-1024x829.jpg\| (c) Zhenglu Li, University of Southern California ~~\|400px \| right~~ ]]		[[File:Tdgw-phonon-usc-01-1024x829.jpg\|thumb\|right\|400px\|(c) Zhenglu Li, University of Southern California]]

	In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).		In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).

FulvioPaleari at 14:45, 13 March 2026

2026-03-13T14:45:50Z

← Older revision		Revision as of 14:45, 13 March 2026
Line 1:		Line 1:
	[[exc-ph scheme\| ~~File:~~Tdgw-phonon-usc-01-1024x829.jpg\| (c) Zhenglu Li, University of Southern California \|400px \| right ]]		[[exc-ph scheme\| Tdgw-phonon-usc-01-1024x829.jpg\| (c) Zhenglu Li, University of Southern California \|400px \| right ]]

	In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).		In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).

FulvioPaleari at 14:45, 13 March 2026

2026-03-13T14:45:40Z

← Older revision		Revision as of 14:45, 13 March 2026
Line 1:		Line 1:
	[[File:Tdgw-phonon-usc-01-1024x829.jpg\| ~~400px \| right \| caption=~~(c) Zhenglu Li, University of Southern California]]		[[exc-ph scheme\| File:Tdgw-phonon-usc-01-1024x829.jpg\| (c) Zhenglu Li, University of Southern California \|400px \| right ]]

	In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).		In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).

FulvioPaleari at 14:44, 13 March 2026

2026-03-13T14:44:44Z

← Older revision		Revision as of 14:44, 13 March 2026
Line 1:		Line 1:
	[[File:Tdgw-phonon-usc-01-1024x829.jpg\| 400px \| right \| ~~Caption~~=(c) Zhenglu Li, University of Southern California]]		[[File:Tdgw-phonon-usc-01-1024x829.jpg\| 400px \| right \| caption=(c) Zhenglu Li, University of Southern California]]

	In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).		In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).

FulvioPaleari at 14:44, 13 March 2026

2026-03-13T14:44:28Z

← Older revision		Revision as of 14:44, 13 March 2026
Line 1:		Line 1:
	[[File:Tdgw-phonon-usc-01-1024x829.jpg\| 400px \| right]]		[[File:Tdgw-phonon-usc-01-1024x829.jpg\| 400px \| right \| Caption=(c) Zhenglu Li, University of Southern California]]

	In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).		In this advanced tutorial, we will calculate exciton-phonon interactions from first principles by interfacing DFPT (for phonon calculations) and BSE (for exciton calculations).

FulvioPaleari: /* Requirements */

2026-03-13T14:40:58Z

Requirements

← Older revision		Revision as of 14:40, 13 March 2026
Line 17:		Line 17:
	Also, we assume that you already know how to run both a basic '''Yambo''' GW-BSE calculation and a DFPT phonon calculation with '''Quantum ESPRESSO'''.		Also, we assume that you already know how to run both a basic '''Yambo''' GW-BSE calculation and a DFPT phonon calculation with '''Quantum ESPRESSO'''.

	Besides the QE executables <code>pw.x</code> and <code>ph.x</code>, we also use the yambo phonon-specific executable <code>yambo_ph</code> and the python utility '''Yambopy'''. The auxiliary code '''LetzElPhC''' (executable <code>lelphc</code>) will be used to obtain the electron-phonon matrix elements by reading the same electronic wavefunctions used by Yambo (and stored in the <code>SAVE</code> directory), while also making full use of crystal symmetries. [https://~~gitlab~~.com/~~lumen~~-code/LetzElPhC LetzElPhC] will be run by Yambopy, but it must nonetheless be installed. Finally, the exciton-phonon properties can be computed either using <code>yambo_ph</code> or using Yambopy itself. Both cases will be covered in this tutorial.		Besides the QE executables <code>pw.x</code> and <code>ph.x</code>, we also use the yambo phonon-specific executable <code>yambo_ph</code> and the python utility '''Yambopy'''. The auxiliary code '''LetzElPhC''' (executable <code>lelphc</code>) will be used to obtain the electron-phonon matrix elements by reading the same electronic wavefunctions used by Yambo (and stored in the <code>SAVE</code> directory), while also making full use of crystal symmetries. [https://github.com/yambo-code/LetzElPhC LetzElPhC] will be run by Yambopy, but it must nonetheless be installed. Finally, the exciton-phonon properties can be computed either using <code>yambo_ph</code> or using Yambopy itself. Both cases will be covered in this tutorial.

	[[File:Workflow scheme.png\|800px\|center]]		[[File:Workflow scheme.png\|800px\|center]]

FulvioPaleari: /* Step 7: Obtain the exciton-phonon coupling */

2026-02-23T17:11:04Z

Step 7: Obtain the exciton-phonon coupling

← Older revision		Revision as of 17:11, 23 February 2026
Line 343:		Line 343:
	wfcs = YamboWFDB(filename='ns.wf',save=savepath,latdb=lattice,bands_range=bands_range)		wfcs = YamboWFDB(filename='ns.wf',save=savepath,latdb=lattice,bands_range=bands_range)
	<span style="color:blue"># Calculate exciton-phonon matrix elements</span>		<span style="color:blue"># Calculate exciton-phonon matrix elements</span>
	exph = exciton_phonon_matelem(lattice,elph,wfcs,BSE_dir=bsepath,~~neigs~~=nexc,dmat_mode='save',exph_file='MoS2_Ex-ph.npy')		exph = exciton_phonon_matelem(lattice,elph,wfcs,BSE_dir=bsepath,nexc_in=nexc,nexc_out=nexc,dmat_mode='save',exph_file='MoS2_Ex-ph.npy')

	In this script, we can select the number exciton states <math>\lambda</math> with <code>nexc</code>, the single-particle bands range with <code>bands_range</code>. '''Please note''': in this case, the band index starts from 0 (python indexing) and the the interval of bands read by the code is <math>[n_i,n_f)</math>, therefore the last value (28 in the example) is excluded. That is, in the example we are selecting the 25th, 26th, 27th and 28th bands. Those bands have to be present in both the electron-phonon and BSE calculations.		In this script, we can select the number exciton states <math>\lambda</math> with <code>nexc</code>, the single-particle bands range with <code>bands_range</code>. '''Please note''': in this case, the band index starts from 0 (python indexing) and the the interval of bands read by the code is <math>[n_i,n_f)</math>, therefore the last value (28 in the example) is excluded. That is, in the example we are selecting the 25th, 26th, 27th and 28th bands. Those bands have to be present in both the electron-phonon and BSE calculations.

FulvioPaleari: /* Analysis of the couplings */

2025-11-20T10:54:11Z

Analysis of the couplings

← Older revision		Revision as of 10:54, 20 November 2025
Line 375:		Line 375:
	First, we select the exciton and phonon states to be included in <code>F_A</code>, together with the path of databases and plot details:		First, we select the exciton and phonon states to be included in <code>F_A</code>, together with the path of databases and plot details:

	# Exciton in states		<span style="color:blue"># Exciton "in" states</span>
	exc_in = [2,3] # First bright peak (A: 2,3 -- B: 6,7)		exc_in = [2,3] <span style="color:blue"># First bright peak (A: 2,3 -- B: 6,7)</span>
	exc_out = [0,1,2,3] # first 4 states (dispersion of dark triplet state and A)		exc_out = [0,1,2,3] <span style="color:blue"># first 4 states (dispersion of dark triplet state and A)</span>
	ph_in = 'all'		ph_in = 'all'
	# Paths of databases		<span style="color:blue"># Paths of databases</span>
	ns_db1 =f'{path}/SAVE/ns.db1'		ns_db1 =f'{path}/SAVE/ns.db1'
	ns_ypy = 'MoS2_Ex-ph.npy'		ns_ypy = 'MoS2_Ex-ph.npy'

	...		...

	Then, we load the data:		Then, we load the data:

	# Read lattice and k-space info		<span style="color:blue"># Read lattice and k-space info</span>
	ylat = YamboLatticeDB.from_db_file(filename=ns_db1)		ylat = YamboLatticeDB.from_db_file(filename=ns_db1)
	print(ylat)		print(ylat)

	# Load exc-ph database		<span style="color:blue"># Load exc-ph database</span>
	X_py = np.load(ns_ypy)		X_py = np.load(ns_ypy)
	G_squared = np.abs(X_py)**2.		G_squared = np.abs(X_py)**2.
Line 405:		Line 405:
	G_squared = G_squared[:, exc_out].sum(axis=(1))		G_squared = G_squared[:, exc_out].sum(axis=(1))

	F_q = np.sqrt( G_squared )*ha2ev # Switch from Ha to eV		F_q = np.sqrt( G_squared )*ha2ev <span style="color:blue"># Switch from Ha to eV</span>

	And finally, we have to make a plotting function. For this tutorial we will use a custom scatterplot employing some of the plotting tools provided by yambopy (but you can do whatever you want).		And finally, we have to make a plotting function. For this tutorial we will use a custom scatterplot employing some of the plotting tools provided by yambopy (but you can do whatever you want).

FulvioPaleari: /* Step 7: Obtain the exciton-phonon coupling */

2025-11-20T10:52:13Z

Step 7: Obtain the exciton-phonon coupling

← Older revision		Revision as of 10:52, 20 November 2025
Line 324:		Line 324:
	Next, we write a python user script importing the yambopy exciton-phonon tools. You can find a version of this script in <code>yambopy/tutorials/exciton-phonon/calculate_excph.py</code>.		Next, we write a python user script importing the yambopy exciton-phonon tools. You can find a version of this script in <code>yambopy/tutorials/exciton-phonon/calculate_excph.py</code>.

	import numpy as np		import numpy as np
	from yambopy import YamboLatticeDB,YamboWFDB,LetzElphElectronPhononDB		from yambopy import YamboLatticeDB,YamboWFDB,LetzElphElectronPhononDB <span style="color:blue">#Specific Yambopy dbs loading classes</span>
	from yambopy.exciton_phonon.excph_matrix_elements import exciton_phonon_matelem		from yambopy.exciton_phonon.excph_matrix_elements import exciton_phonon_matelem <span style="color:blue">#Specific exc-ph functions</span>

	path = '1L_MoS2'		path = '1L_MoS2'
	bands_range=[24,28] # 2 valence bands, 2 conduction bands		bands_range=[24,28] <span style="color:blue"># 2 valence bands, 2 conduction bands</span>
	nexc = 12 # number of excitonic states		nexc = 12 <span style="color:blue"># number of excitonic states</span>

	bsepath = f'{path}/bse-allq_full' # Path to BSE calculation (Lin=Lout)		bsepath = f'{path}/bse-allq_full' <span style="color:blue"># Path to BSE calculation (Lin=Lout)</span>
	savepath = f'{path}/SAVE' # Yambo SAVE		savepath = f'{path}/SAVE' <span style="color:blue"># Yambo SAVE</span>
	ndb_elph = f'{path}/ndb.elph' # LetzElPhC electron-phonon database (any convention)		ndb_elph = f'{path}/ndb.elph' <span style="color:blue"># LetzElPhC electron-phonon database (any convention)</span>

	# Read lattice		<span style="color:blue"># Read lattice</span>
	lattice = YamboLatticeDB.from_db_file(filename=f'{savepath}/ns.db1')		lattice = YamboLatticeDB.from_db_file(filename=f'{savepath}/ns.db1')
	# Read electron-phonon		<span style="color:blue"># Read electron-phonon</span>
	elph = LetzElphElectronPhononDB(ndb_elph,read_all=False)		elph = LetzElphElectronPhononDB(ndb_elph,read_all=False)
	# Read wave functions		<span style="color:blue"># Read wave functions</span>
	wfcs = YamboWFDB(filename='ns.wf',save=savepath,latdb=lattice,bands_range=bands_range)		wfcs = YamboWFDB(filename='ns.wf',save=savepath,latdb=lattice,bands_range=bands_range)
	# Calculate exciton-phonon matrix elements		<span style="color:blue"># Calculate exciton-phonon matrix elements</span>
	exph = exciton_phonon_matelem(lattice,elph,wfcs,BSE_dir=bsepath,neigs=nexc,dmat_mode='save',exph_file='MoS2_Ex-ph.npy')		exph = exciton_phonon_matelem(lattice,elph,wfcs,BSE_dir=bsepath,neigs=nexc,dmat_mode='save',exph_file='MoS2_Ex-ph.npy')