Time-dependent density functional theory (standard kernel) - Revision history

Conor: /* Prerequisites */

2019-11-07T09:36:15Z

Prerequisites

← Older revision		Revision as of 09:36, 7 November 2019
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	== Prerequisites ==		== Prerequisites ==
			[[File:Yambo-handbook-v4.1.2-p-5.png\|thumb\|Cheatsheet on TDDFT\|150px]]
	* You must first complete the "How to use Yambo" and the "Optics at the independent particle level" and "local fields" modules		* You must first complete the "How to use Yambo" and the "Optics at the independent particle level" and "local fields" modules

Myrta: /* Optics runlevel */

2017-04-16T18:33:10Z

Optics runlevel

← Older revision		Revision as of 18:33, 16 April 2017
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	gnuplot> plot "o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:2 w l t 'ALDA',"o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:4 w l t 'IPA'		gnuplot> plot "o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:2 w l t 'ALDA',"o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:4 w l t 'IPA'

	[[File:~~3D_ALDA-hBN~~.png\|none\|500px\|Yambo tutorial image]]		[[File:3D_ALDA_hBN.png\|none\|500px\|Yambo tutorial image]]

	What is clear from this plot is that the ALDA kernel does not significantly change the optical spectrum when compared with the independent particle level of approximation (IPA). The same trend can be observed for other semiconductors and insulators.		What is clear from this plot is that the ALDA kernel does not significantly change the optical spectrum when compared with the independent particle level of approximation (IPA). The same trend can be observed for other semiconductors and insulators.

Myrta: /* Links */

2017-04-16T18:32:23Z

Links

← Older revision		Revision as of 18:32, 16 April 2017
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	== Links ==		== Links ==
	* Next module: [[~~Long~~-range corrected ~~kernel (standard~~ kernel)\|Long-range corrected kernel]]		* Next module: [[Time-dependent density functional theory (long-range corrected kernel) \| Long-range corrected kernel]]
	* [[Tutorials\|Back to tutorials menu]]		* [[Tutorials\|Back to tutorials menu]]

Myrta: /* Choosing input parameters */

2017-04-16T18:13:53Z

Choosing input parameters

← Older revision		Revision as of 18:13, 16 April 2017
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	== Choosing input parameters ==		== Choosing input parameters ==
	Enter the folder for bulk hBN that contains the SAVE directory, and generate the input file. From <code>yambo -H</code> you should understand that the correct option is <code>yambo -o c -k <opt> </code>.		Enter the folder for bulk hBN that contains the SAVE directory, and generate the input file. From <code>yambo -H</code> you should understand that the correct option is <code>yambo -o c -k <opt> </code>.
	Where <opt> can be 'hartree' as in the tutorial on the [[Local fields\|local fields]], or 'alda' or 'lrc' respectively for the ALDA and LRC approximations for the xc kernel outlined above.		Where <opt> can be 'hartree' as in the tutorial on the [[Local fields\|local fields]], or 'alda' or 'lrc' ([[Time-dependent density functional theory (long-range corrected kernel)\|see next tutorial]]) respectively for the ALDA and LRC approximations for the xc kernel outlined above.
	Let's start by ~~running~~ the calculation with the ALDA kernel:		Let's start by generating the input for a calculation with the ALDA kernel:
	$ cd YAMBO_TUTORIALS/hBN-3D/YAMBO		$ cd YAMBO_TUTORIALS/hBN-3D/YAMBO
	$ yambo ''(Initialization)''		$ yambo ''(Initialization)''

Myrta: /* Optics runlevel */

2017-04-16T17:58:32Z

Optics runlevel

← Older revision		Revision as of 17:58, 16 April 2017
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	gnuplot> plot "o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:2 w l t 'ALDA',"o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:4 w l t 'IPA'		gnuplot> plot "o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:2 w l t 'ALDA',"o-3D_ALDA.eps_q1_inv_alda_dyson" u 1:4 w l t 'IPA'

	Yambo tutorial image		[[File:3D_ALDA-hBN.png\|none\|500px\|Yambo tutorial image]]

	What is clear from this plot is that the ALDA kernel does not significantly change the optical spectrum when compared with the independent particle level of approximation (IPA). The same trend can be observed for other semiconductors and insulators.		What is clear from this plot is that the ALDA kernel does not significantly change the optical spectrum when compared with the independent particle level of approximation (IPA). The same trend can be observed for other semiconductors and insulators.

Myrta: /* Optics runlevel */

2017-04-16T17:55:52Z

Optics runlevel

← Older revision		Revision as of 17:55, 16 April 2017
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	Note that, with respect to the Hartree kernel (RPA calculations) the libxc is called to calculate the xc kernel within the ALDA, in particular the Perdew-Zunger parametrization for the correlation part of the LDA is used.		Note that, with respect to the Hartree kernel (RPA calculations) the libxc is called to calculate the xc kernel within the ALDA, in particular the Perdew-Zunger parametrization for the correlation part of the LDA is used.

	~~let~~'s compare the absorption with and without the local fields included. By inspecting the o-~~q100~~.eps_q1_inv_rpa_dyson file we find that this information is given in the 2nd and 4th columns, respectively:		Let's compare the absorption with and without the ALDA (+ local fields) included. By inspecting the o-3D-ALDA.eps_q1_inv_rpa_dyson file we find that this information is given in the 2nd and 4th columns, respectively:

	$ head -n30 o-3D_ALDA.eps_q1_inv_alda_dyson		$ head -n30 o-3D_ALDA.eps_q1_inv_alda_dyson
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	Yambo tutorial image		Yambo tutorial image

			What is clear from this plot is that the ALDA kernel does not significantly change the optical spectrum when compared with the independent particle level of approximation (IPA). The same trend can be observed for other semiconductors and insulators.

	==Summary==		==Summary==

Myrta: /* Choosing input parameters */

2017-04-16T17:50:45Z

Choosing input parameters

← Older revision		Revision as of 17:50, 16 April 2017
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	[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc		[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc
	[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size		[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size
	[[Variables#NGsBlkXd\|NGsBlkXd]]= ~~'''~~ 3 Ry~~'''~~ # [Xd] Response block size		[[Variables#NGsBlkXd\|NGsBlkXd]]= 3 Ry # [Xd] Response block size
	% [[Variables#QpntsRXd\|QpntsRXd]]		% [[Variables#QpntsRXd\|QpntsRXd]]
	1 \| 1 \| # [Xd] Transferred momenta		1 \| 1 \| # [Xd] Transferred momenta
	%		%
	% [[Variables#EnRngeXd\|EnRngeXd]]		% [[Variables#EnRngeXd\|EnRngeXd]]
	0.00000 \| 20.00000 \| eV # [Xd] Energy range		0.00000 \| 10.00000 \| eV # [Xd] Energy range
	%		%
	% [[Variables#DmRngeXd\|DmRngeXd]]		% [[Variables#DmRngeXd\|DmRngeXd]]
	0.200000 \| 0.200000 \| eV # [Xd] Damping range		0.200000 \| 0.200000 \| eV # [Xd] Damping range
	%		%
	[[Variables#ETStpsXd\|ETStpsXd]]= ~~2001~~ # [Xd] Total Energy steps		[[Variables#ETStpsXd\|ETStpsXd]]= 1001 # [Xd] Total Energy steps
	% [[Variables#LongDrXd\|LongDrXd]]		% [[Variables#LongDrXd\|LongDrXd]]
	1.000000 \| 1.000000 \| 0.000000 \| # [Xd] [cc] Electric Field		1.000000 \| 1.000000 \| 0.000000 \| # [Xd] [cc] Electric Field

Myrta at 17:10, 16 April 2017

2017-04-16T17:10:07Z

← Older revision		Revision as of 17:10, 16 April 2017
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	In this ~~tutorial~~ you will learn how to calculate optical spectra at the time-dependent density-functional theory level for bulk hBN.		In this module you will learn how to calculate optical spectra at the time-dependent density-functional theory level for bulk hBN.
	== Background ==		== Background ==
	~~The macroscopic dielectric function is obtained by including the so-called local field effects (LFE) in the calculation of the response function.~~ Within the time-dependent DFT formalism ~~this~~ is ~~achieved~~ by solving the Dyson equation for the susceptibility ''X''. In reciprocal space this is given by:		Within the time-dependent DFT formalism the macroscopic dielectric function [[Local_fields\|is obtained]] by solving the Dyson equation for the susceptibility ''X''. In reciprocal space this is given by:
	[[File:Yambo-CH7.png\|none\|x50px\|Yambo tutorial image]]		[[File:Yambo-CH7.png\|none\|x50px\|Yambo tutorial image]]
	~~The microscopic dielectric function is related to ''X'' by:~~
	~~[[File:Yambo-CH5.png\|none\|x30px\|Yambo tutorial image]]~~
	~~and the macroscopic dielectric function is obtained by taking the (0,0) component of the inverse microscopic one:~~
	~~[[File:Yambo-CH6.png\|none\|x50px\|Yambo tutorial image]]~~
	~~Experimental observables like the optical absorption and the electron energy loss can be obtained from the macroscopic dielectric function:~~
	~~[[File:Yambo-CH8.png\|none\|x50px\|Yambo tutorial image]]~~

	The ''f <sup> xc</sup>'' term is called the exchange-correlation (xc) kernel and describes the response of the xc potential at a time ''t'' to changes in the density at all previous times. Approximations		The ''f <sup> xc</sup>'' term is called the exchange-correlation (xc) kernel and describes the response of the xc potential at a time ''t'' to changes in the density at all previous times. Approximations
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	Within this family we consider here the adiabatic local density approximation (ALDA)		Within this family we consider here the adiabatic local density approximation (ALDA)
	[[File:Eq_ALDA.png\|none\|x50px]]		[[File:Eq_ALDA.png\|none\|x50px]]

	~~As this module will show for bulk hBN this approximation provides spectra similar to the RPA when applied to extended systems (it has instead a significant impact on molecular excitations).~~
	One of the main problems that has been pinpointed in the literature is that ALDA and its likes miss a long range contribution essential to reproduce excitations in solids. Several approximations have been proposed to introduce this essential long range contribution.<ref>L. Reining, V. Olevano, A. Rubio, and G. Onida, Phys. Rev. Lett. 88, 066404 (2002)</ref><ref>P. E. Trevisanutto, A. Terentjevs, L. A. Constantin, V. Olevano, and F. Della Sala, Physical Review B 87, 205143 (2013)</ref><ref>J. A. Berger, Phys. Rev. Lett. 115, 137402 (2015)</ref><ref>S. Rigamonti, S. Botti, V. Veniard, C. Draxl, L. Reining, and F. Sottile, Phys. Rev. Lett. 114, 146402 (2015)</ref><ref>S. Sharma, J. K. Dewhurst, A. Sanna, and E. K. U. Gross, Phys. Rev. Lett. 107, 186401 (2011)</ref>

	~~Within this family we consider here the long-range correction approximation (LRC):~~
	~~[[File:Eq_LRC.png\|none\|x40px]]~~
	where α is an empirical parameter related to the system screening.<ref>S. Botti, F. Sottile, N. Vast, V. Olevano, L. Reining, H.-C.Weissker, A. Rubio, G. Onida, R. Del Sole, and R. Godby, Physical Review B 69, 155112 (2004)</ref>

	Note that approximations of this form cannot be rigorously justified within the sole time-dependent density-functional framework. Additional key quantities such as the electron density current or the macroscopic polarization (together with the corresponding xc fields) need to be considered.<ref>M. Gr¨ning, D. Sangalli, C. Attaccalite, C. Physical Review B '''94''', 035149 (2016)</ref><ref>P. L. de Boeij, F. Kootstra, J. A. Berger, R. van Leeuwen, and J. G. Snijders, The Journal of Chemical Physics 115, 1995 (2001)</ref><ref>J. A. Berger, Phys. Rev. Lett. 115, 137402 (2015)</ref>

	== Prerequisites ==		== Prerequisites ==
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	* <code>gnuplot</code>, for plotting spectra		* <code>gnuplot</code>, for plotting spectra

	== Choosing input parameters~~: ALDA kernel~~ ==		== Choosing input parameters ==
	Enter the folder for bulk hBN that contains the SAVE directory, and generate the input file. From <code>yambo -H</code> you should understand that the correct option is <code>yambo -o c -k <opt> </code>.		Enter the folder for bulk hBN that contains the SAVE directory, and generate the input file. From <code>yambo -H</code> you should understand that the correct option is <code>yambo -o c -k <opt> </code>.
	Where <opt> can be 'hartree' as in the tutorial on the [[Local fields\|local fields]], or 'alda' or 'lrc' respectively for the ALDA and LRC approximations for the xc kernel outlined above.		Where <opt> can be 'hartree' as in the tutorial on the [[Local fields\|local fields]], or 'alda' or 'lrc' respectively for the ALDA and LRC approximations for the xc kernel outlined above.
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	$ cd YAMBO_TUTORIALS/hBN-3D/YAMBO		$ cd YAMBO_TUTORIALS/hBN-3D/YAMBO
	$ yambo ''(Initialization)''		$ yambo ''(Initialization)''
	$ yambo -F yambo.in_ALDA ~~-V RL~~ -J 3D_ALDA -o c -k alda		$ yambo -F yambo.in_ALDA -J 3D_ALDA -o c -k alda
	We thus use a new input file ''yambo.in_ALDA'', switch on the <code>FFTGvecs</code> variable, and label all outputs/databases with a ''3D_ALDA'' tag. Make sure to set/modify all of the following variables to:		We thus use a new input file ''yambo.in_ALDA'', switch on the <code>FFTGvecs</code> variable, and label all outputs/databases with a ''3D_ALDA'' tag. Make sure to set/modify all of the following variables to:
	~~[[Variables#FFTGvecs\|FFTGvecs]]= '''30 Ry''' # [FFT] Plane-waves~~
	[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc		[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc
	[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size		[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size
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	* The ALDA kernel, and expanded G-vectors in the screening and in the xc kernel up to 3 Ry (about 85 G-vectors)		* The ALDA kernel, and expanded G-vectors in the screening and in the xc kernel up to 3 Ry (about 85 G-vectors)

	==Optics runlevel~~: ALDA~~==		==Optics runlevel==
	Save the input file and launch the code, keeping the command line options as before (i.e., just remove the lower case options):		Save the input file and launch the code, keeping the command line options as before (i.e., just remove the lower case options):
	$ yambo -F yambo.in_ALDA -J 3D_ALDA		$ yambo -F yambo.in_ALDA -J 3D_ALDA
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	==Summary==		==Summary==
	From this tutorial you've learned:		From this tutorial you've learned:
	* How to compute ~~a simple~~ optical spectrum		* How to compute an optical spectrum within the adiabatic local density approximation
	* How to reduce the ~~computational load through reducing the G-vector/energy cut off and removing the Vnl term~~
	* How to plot different components of the dielectric tensor
	* How to use the <code>-J</code> option to neatly label and organise files and databases

	== Links ==		== Links ==
	* Next module: [[~~Local fields~~\|~~Local fields~~]]		* Next module: [[Long-range corrected kernel (standard kernel)\|Long-range corrected kernel]]
	* Back to [[First steps: a walk through from DFT to optical properties\|First steps with yambo]] tutorial
	* [[Tutorials\|Back to tutorials menu]]		* [[Tutorials\|Back to tutorials menu]]

	~~== References ==~~

Myrta: Myrta moved page Time-dependent density functional theory to Time-dependent density functional theory (standard kernel)

2017-04-16T16:16:48Z

Myrta moved page Time-dependent density functional theory to Time-dependent density functional theory (standard kernel)

← Older revision	Revision as of 16:16, 16 April 2017
(No difference)

Myrta at 16:15, 16 April 2017

2017-04-16T16:15:43Z

@@ Line 64: / Line 64: @@
 * The ALDA kernel, and expanded G-vectors in the screening and in the xc kernel up to 3 Ry (about 85 G-vectors)
-==Optics runlevel==
+==Optics runlevel: ALDA==
 Save the input file and launch the code, keeping the command line options as before (i.e., just remove the lower case options):
   $ yambo -F yambo.in_ALDA -J 3D_ALDA
@@ Line 90: / Line 90: @@
 Yambo tutorial image
 ==Summary==

← Older revision		Revision as of 17:50, 16 April 2017
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	[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc		[[Variables#Chimod\|Chimod]]= "ALDA" # [X] IP/Hartree/ALDA/LRC/BSfxc
	[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size		[[Variables#FxcGRLc\|FxcGRLc]]= ''' 3 Ry''' # [Xd] Response block size
	[[Variables#NGsBlkXd\|NGsBlkXd]]= ~~'''~~ 3 Ry~~'''~~ # [Xd] Response block size		[[Variables#NGsBlkXd\|NGsBlkXd]]= 3 Ry # [Xd] Response block size
	% [[Variables#QpntsRXd\|QpntsRXd]]		% [[Variables#QpntsRXd\|QpntsRXd]]
	1 \| 1 \| # [Xd] Transferred momenta		1 \| 1 \| # [Xd] Transferred momenta
	%		%
	% [[Variables#EnRngeXd\|EnRngeXd]]		% [[Variables#EnRngeXd\|EnRngeXd]]
	0.00000 \| 20.00000 \| eV # [Xd] Energy range		0.00000 \| 10.00000 \| eV # [Xd] Energy range
	%		%
	% [[Variables#DmRngeXd\|DmRngeXd]]		% [[Variables#DmRngeXd\|DmRngeXd]]
	0.200000 \| 0.200000 \| eV # [Xd] Damping range		0.200000 \| 0.200000 \| eV # [Xd] Damping range
	%		%
	[[Variables#ETStpsXd\|ETStpsXd]]= ~~2001~~ # [Xd] Total Energy steps		[[Variables#ETStpsXd\|ETStpsXd]]= 1001 # [Xd] Total Energy steps
	% [[Variables#LongDrXd\|LongDrXd]]		% [[Variables#LongDrXd\|LongDrXd]]
	1.000000 \| 1.000000 \| 0.000000 \| # [Xd] [cc] Electric Field		1.000000 \| 1.000000 \| 0.000000 \| # [Xd] [cc] Electric Field