Calculating the electric field gradient - Revision history

Huebsch: /* Step-by-step instructions */

2026-03-17T08:12:57Z

Step-by-step instructions

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	The electric field gradient is calculated post-self-consistent field (post-SCF) using {{TAG\|LEFG}}. A well-converged SCF calculation is therefore crucial. The electric field gradient is very sensitive to several input parameters that must all be independently tested. In particular, small differences in the structure can make big differences to <math>V_{zz}</math>, up to 50 % {{Cite\|petrilli:prb:1998}}; see the Advice section for more details. Make sure to have a well-optimized structure before you begin the convergence tests.		The electric field gradient is calculated post-self-consistent field (post-SCF) using {{TAG\|LEFG}}. A well-converged SCF calculation is therefore crucial. The electric field gradient is very sensitive to several input parameters that must all be independently tested. In particular, small differences in the structure can make big differences to <math>V_{zz}</math>, up to 50 % {{Cite\|petrilli:prb:1998}}; see the Advice section for more details. Make sure to have a well-optimized structure before you begin the convergence tests.

	~~'''~~Step 1 (optional):~~'''~~ Calculate the ~~chemical shielding~~ using a previously converged calculation		=== Step 1 (optional): Calculate the electric field gradient using a previously converged calculation ===

	Since the chemical shielding is calculated post-SCF, you can use a previously converged {{FILE\|WAVECAR}} with {{TAG\|ISTART}} = 1 and {{TAG\|NELM}} = 1. The corresponding density, {{TAG\|CHGCAR}} is calculated from the {{FILE\|WAVECAR}} file before the first elementary step so it need not be included.		Since the chemical shielding is calculated post-SCF, you can use a previously converged {{FILE\|WAVECAR}} with {{TAG\|ISTART}} = 1 and {{TAG\|NELM}} = 1. The corresponding density, {{TAG\|CHGCAR}} is calculated from the {{FILE\|WAVECAR}} file before the first elementary step so it need not be included.

	~~'''~~Step 2a:~~'''~~ Define the nuclear quadrupolar moments		=== Step 2a: Define the nuclear quadrupolar moments ===

	The calculated electric field gradients are not observable in experiment. Instead, the quadrupolar coupling constant can be calculated so long as the nuclear quadrupolar moments are defined in {{TAG\|QUAD_EFG}}. Each species in your {{FILE\|POSCAR}} file should be defined; there is no need to define each individual ion. A short table of values can be found in Ref. {{Cite\|pyykko:molphys:2017}}.		The calculated electric field gradients are not observable in experiment. Instead, the quadrupolar coupling constant can be calculated so long as the nuclear quadrupolar moments are defined in {{TAG\|QUAD_EFG}}. Each species in your {{FILE\|POSCAR}} file should be defined; there is no need to define each individual ion. A short table of values can be found in Ref. {{Cite\|pyykko:molphys:2017}}.

	~~'''~~Step 2b (optional):~~'''~~ Determine a suitable energetic break value		=== Step 2b (optional): Determine a suitable energetic break value ===

	The break condition for the self-consistency step {{TAG\|EDIFF}} strongly influences the chemical shielding. A setting of {{TAG\|EDIFF}} = 1E-8 eV is generally recommended. Convergence is taken to be within 0.1 ppm.		The break condition for the self-consistency step {{TAG\|EDIFF}} strongly influences the chemical shielding. A setting of {{TAG\|EDIFF}} = 1E-8 eV is generally recommended. Convergence is taken to be within 0.1 ppm.

	~~'''~~Step 3:~~'''~~ Converge the plane-wave energy cutoff		=== Step 3: Converge the plane-wave energy cutoff ===

	A large plane-wave energy cutoff is required to fully converge the electric field gradient. Perform multiple calculations while increasing the basis set size, as defined in {{TAG\|ENCUT}}, incrementally (e.g., by 100 eV intervals). Convergence should be aimed to be within 3 significant figures, although this will not be feasible for heavier elements.		A large plane-wave energy cutoff is required to fully converge the electric field gradient. Perform multiple calculations while increasing the basis set size, as defined in {{TAG\|ENCUT}}, incrementally (e.g., by 100 eV intervals). Convergence should be aimed to be within 3 significant figures, although this will not be feasible for heavier elements.

	~~'''~~Step 4:~~'''~~ Converge the '''k''' point mesh		=== Step 4: Converge the '''k''' point mesh ===

	Similar to the basis, the '''k''' point mesh can strongly influence the coupling constant. The '''k''' point mesh should be increased incrementally, i.e., 1x1x1, 2x2x2, 3x3x3, until convergence within 3 significant figures is achieved. It is only necessary to converge the '''k''' point mesh for crystals, gas-phase molecules should use the Γ-point only.		Similar to the basis, the '''k''' point mesh can strongly influence the coupling constant. The '''k''' point mesh should be increased incrementally, i.e., 1x1x1, 2x2x2, 3x3x3, until convergence within 3 significant figures is achieved. It is only necessary to converge the '''k''' point mesh for crystals, gas-phase molecules should use the Γ-point only.

	~~'''~~Step 5:~~'''~~ Compare to experiment		=== Step 5: Compare to experiment ===

	The purpose of these calculations is to compare directly to experiment. The EFG that has been calculated is not directly measurable but the quadrupolar coupling constants ''C<sub>q</sub>'' are.		The purpose of these calculations is to compare directly to experiment. The EFG that has been calculated is not directly measurable but the quadrupolar coupling constants ''C<sub>q</sub>'' are.

Huebsch at 10:20, 16 March 2026

2026-03-16T10:20:57Z

← Older revision		Revision as of 10:20, 16 March 2026
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	{{TAGBL\|LEFG}} = .TRUE.		{{TAGBL\|LEFG}} = .TRUE.
	{{TAGBL\|QUAD_EFG}} = 0. -696. 20.44 0. 2.860 # Nuclear quadrupolar moments for Pb I N O D		{{TAGBL\|QUAD_EFG}} = 0. -696. 20.44 0. 2.860 # Nuclear quadrupolar moments for Pb I N O D
			{{TAGBL\|LNMRCAR}} = .TRUE.

	Script to loop through {{TAG\|EDIFF}} from 1E-4 eV to 1E-8 eV:		Script to loop through {{TAG\|EDIFF}} from 1E-4 eV to 1E-8 eV:

Singraber at 08:11, 24 October 2025

2025-10-24T08:11:34Z

← Older revision		Revision as of 08:11, 24 October 2025
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	=Example scripts for convergence tests=		=Example scripts for convergence tests=
	Several tests are necessary to obtain various NMR parameters. Make sure to change the example {{FILE\|INCAR}} files to include the tags for your desired calculation. We provide some example scripts below:		Several tests are necessary to obtain various NMR parameters. Make sure to change the example {{FILE\|INCAR}} files to include the tags for your desired calculation. We provide some example scripts below:
	{{NB\|important\|Make sure to replace the {{~~TAGO~~\|QUAD_EFG}} in the {{FILE\|INCAR}} with the values for the isotopes in your system.}}		{{NB\|important\|Make sure to replace the {{TAG\|QUAD_EFG}} in the {{FILE\|INCAR}} with the values for the isotopes in your system.}}

	==Energetic break criterion tests==		==Energetic break criterion tests==

Csheldon: /* Related tags and articles */

2025-05-12T11:39:31Z

Csheldon at 11:37, 12 May 2025

2025-05-12T11:37:06Z

← Older revision		Revision as of 11:37, 12 May 2025
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	done		done
	</pre>		</pre>

			== Related tags and articles ==
			{{TAG\|LEFG}}
			{{TAG\|QUAD_EFG}}

	==References==		==References==

	[[Category:Howto]][[Category:NMR]]		[[Category:Howto]][[Category:NMR]]

Csheldon: /* PAW pseudopotentials */

2025-03-26T08:13:24Z

PAW pseudopotentials

← Older revision		Revision as of 08:13, 26 March 2025
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	===PAW pseudopotentials===		===PAW pseudopotentials===
	The standard [[:Category:Pseudopotentials\|PAW pseudopotentials]] {{FILE\|POTCAR}} used are sufficient for calculating the electric field gradient. Using [[Available pseudopotentials\|GW pseudopotentials]] can significantly improve results. Semi-core electrons can be important, so {{TAG\|~~POSCAR~~}} files with ''_pv'' or ''_sv'' can improve the results, as will the explicit inclusion of augmentation channels with <math>d</math>-projectors.		The standard [[:Category:Pseudopotentials\|PAW pseudopotentials]] {{FILE\|POTCAR}} used are sufficient for calculating the electric field gradient. Using [[Available pseudopotentials\|GW pseudopotentials]] can significantly improve results. Semi-core electrons can be important, so {{TAG\|POTCAR}} files with ''_pv'' or ''_sv'' can improve the results, as will the explicit inclusion of augmentation channels with <math>d</math>-projectors.

	===Additional tags===		===Additional tags===

Csheldon at 12:25, 25 March 2025

2025-03-25T12:25:34Z

← Older revision		Revision as of 12:25, 25 March 2025
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	Nuclei with a spin > ± ½ are called quadrupolar nuclei. They have a non-spherical shape and therefore a non-zero ~~[[Electric Field Gradient\|~~electric field gradient]] (EFG) at the nucleus. The EFG is calculated using {{TAG\|LEFG}} {{Cite\|petrilli:prb:1998}}. By including the quadrupole moment of the isotopes, the quadrupole coupling constants ''C<sub>q</sub>'' can be calculated (multiple definitions exist in the literature, ensure that you are correctly comparing). These are measured using nuclear quadrupole resonance (NQR) spectroscopy, a type of zero- to ultralow-field (ZULF) NMR, NMR, and Mössbauer spectroscopy. The theory is covered in the [[:Category:NMR\|NMR category page]] and {{TAG\|LEFG}} page.		Nuclei with a spin > ± ½ are called quadrupolar nuclei. They have a non-spherical shape and therefore a non-zero electric field gradient (EFG) at the nucleus. The EFG is calculated using {{TAG\|LEFG}} {{Cite\|petrilli:prb:1998}}. By including the quadrupole moment of the isotopes, the quadrupole coupling constants ''C<sub>q</sub>'' can be calculated (multiple definitions exist in the literature, ensure that you are correctly comparing). These are measured using nuclear quadrupole resonance (NQR) spectroscopy, a type of zero- to ultralow-field (ZULF) NMR, NMR, and Mössbauer spectroscopy. The theory is covered in the [[:Category:NMR\|NMR category page]] and {{TAG\|LEFG}} page.

	==Step-by-step instructions==		==Step-by-step instructions==

Csheldon: /* References */

2025-03-19T09:44:39Z

References

← Older revision		Revision as of 09:44, 19 March 2025
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	==References==		==References==

	~~<!--~~ [[Category:Howto]][[Category:NMR]] ~~--!>~~		[[Category:Howto]][[Category:NMR]]

Csheldon: Csheldon moved page Construction:Calculating the electric field gradient to Calculating the electric field gradient

2025-03-10T09:30:51Z

Csheldon moved page Construction:Calculating the electric field gradient to Calculating the electric field gradient

← Older revision	Revision as of 09:30, 10 March 2025
(No difference)

Csheldon at 18:14, 7 March 2025

2025-03-07T18:14:25Z

← Older revision		Revision as of 18:14, 7 March 2025
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	Nuclei with a spin > ± ½ are called quadrupolar nuclei. They have a non-spherical shape and therefore a non-zero [[Electric Field Gradient\|electric field gradient]] (EFG) at the nucleus. The EFG is calculated using {{TAG\|LEFG}} {{Cite\|petrilli:prb:1998}}. By including the quadrupole moment of the isotopes, the quadrupole coupling constants ''C<sub>q</sub>'' can be calculated (multiple definitions exist in the literature, ensure that you are correctly comparing). These are measured using nuclear quadrupole resonance (NQR) spectroscopy, a type of zero- to ultralow-field (ZULF) NMR. The theory is covered in the [[:Category:NMR\|NMR category page]] and {{TAG\|LEFG}} page.		Nuclei with a spin > ± ½ are called quadrupolar nuclei. They have a non-spherical shape and therefore a non-zero [[Electric Field Gradient\|electric field gradient]] (EFG) at the nucleus. The EFG is calculated using {{TAG\|LEFG}} {{Cite\|petrilli:prb:1998}}. By including the quadrupole moment of the isotopes, the quadrupole coupling constants ''C<sub>q</sub>'' can be calculated (multiple definitions exist in the literature, ensure that you are correctly comparing). These are measured using nuclear quadrupole resonance (NQR) spectroscopy, a type of zero- to ultralow-field (ZULF) NMR, NMR, and Mössbauer spectroscopy. The theory is covered in the [[:Category:NMR\|NMR category page]] and {{TAG\|LEFG}} page.

	==Step-by-step instructions==		==Step-by-step instructions==

← Older revision		Revision as of 10:20, 16 March 2026
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	{{TAGBL\|LEFG}} = .TRUE.		{{TAGBL\|LEFG}} = .TRUE.
	{{TAGBL\|QUAD_EFG}} = 0. -696. 20.44 0. 2.860 # Nuclear quadrupolar moments for Pb I N O D		{{TAGBL\|QUAD_EFG}} = 0. -696. 20.44 0. 2.860 # Nuclear quadrupolar moments for Pb I N O D
			{{TAGBL\|LNMRCAR}} = .TRUE.

	Script to loop through {{TAG\|EDIFF}} from 1E-4 eV to 1E-8 eV:		Script to loop through {{TAG\|EDIFF}} from 1E-4 eV to 1E-8 eV:

← Older revision		Revision as of 11:39, 12 May 2025
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	== Related tags and articles ==		== Related tags and articles ==
	{{TAG\|LEFG}}		{{TAG\|LEFG}},
	{{TAG\|QUAD_EFG}}		{{TAG\|QUAD_EFG}}