Calculating the chemical shieldings - Revision history

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

2026-03-17T08:13:51Z

Step-by-step instructions

← Older revision		Revision as of 08:13, 17 March 2026
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	The chemical shielding is calculated post-self-consistent field (post-SCF) using {{TAG\|LCHIMAG}}. A well-converged SCF calculation is therefore crucial. The chemical shielding is very sensitive to several input parameters that must all be independently tested.		The chemical shielding is calculated post-self-consistent field (post-SCF) using {{TAG\|LCHIMAG}}. A well-converged SCF calculation is therefore crucial. The chemical shielding is very sensitive to several input parameters that must all be independently tested.

	~~'''~~Step 1 (optional):~~'''~~ Calculate the chemical shielding using a previously converged calculation		=== Step 1 (optional): Calculate the chemical shielding 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 2 (optional):~~'''~~ Determine a suitable energetic break value		=== Step 2 (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 basis		=== Step 3: Converge the plane-wave basis ===

	A large plane-wave energy cutoff is required to fully converge the chemical shieldings. 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 0.1 ppm, although this will not be feasible for heavier elements.		A large plane-wave energy cutoff is required to fully converge the chemical shieldings. 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 0.1 ppm, 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 chemical shielding. The '''k''' point mesh should be increased incrementally, i.e., 1x1x1, 2x2x2, 3x3x3, until convergence within 0.1 ppm 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 chemical shielding. The '''k''' point mesh should be increased incrementally, i.e., 1x1x1, 2x2x2, 3x3x3, until convergence within 0.1 ppm 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 to experiment. However, the calculated absolute chemical shieldings are not directly comparable to the measured chemical shift due to the lack of a reference. To avoid bias from any single calculation, a series of calculated and their corresponding experimental values are used. The experimental chemical shifts are plotted against the calculated chemical shieldings as is found in Fig. 3 of Ref. {{Cite\|dewijs:laskowski:jcp:2017}}.		The purpose of these calculations is to compare to experiment. However, the calculated absolute chemical shieldings are not directly comparable to the measured chemical shift due to the lack of a reference. To avoid bias from any single calculation, a series of calculated and their corresponding experimental values are used. The experimental chemical shifts are plotted against the calculated chemical shieldings as is found in Fig. 3 of Ref. {{Cite\|dewijs:laskowski:jcp:2017}}.

Huebsch: /* Additional tags */

2026-03-17T08:10:24Z

Additional tags

← Older revision		Revision as of 08:10, 17 March 2026
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	Calculating the chemical shift can also be sped up by utilizing parallelisation. If you are using multiple k-points, then you can treat these in parallel using {{TAG\|KPAR}}, reducing the overall calculation time.		Calculating the chemical shift can also be sped up by utilizing parallelisation. If you are using multiple k-points, then you can treat these in parallel using {{TAG\|KPAR}}, reducing the overall calculation time.
	{{NB\|important\|The treatment of the orbital magnetism ~~is non-relativistic. This~~ is suitable for light nuclei.		{{NB\|important\|The non-relativistic treatment of the orbital magnetism is suitable for light nuclei.
	The ~~standard POTCARs~~ are scalar-relativistic ~~and~~ account ~~partially~~ for relativistic ~~effects.~~		The [[pseudopotentials]] are scalar-relativistic. To account for regularization within scalar-relativistic ZORA use {{TAG\|LZORA}} and to account for spin-orbit coupling use {{TAG\|LSOSHIFT}}.}}
	~~The accuracy can be improved using~~ {{TAG\|~~LBONE~~}}~~, which restores the small B-component of the wave function inside the PAW spheres.~~
	~~Spin~~-orbit coupling ~~is not implemented for chemical shift calculations~~.}}

	=Example scripts for convergence tests=		=Example scripts for convergence tests=

Huebsch: /* Energetic break criterion tests */

2026-03-16T10:20:12Z

Energetic break criterion tests

← Older revision		Revision as of 10:20, 16 March 2026
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	{{TAGBL\|ICHIBARE}} = 1		{{TAGBL\|ICHIBARE}} = 1
	{{TAGBL\|LNMR_SYM_RED}} = .TRUE.		{{TAGBL\|LNMR_SYM_RED}} = .TRUE.
	{{TAGBL\|NLSPLINE}} = .TRUE.		{{TAGBL\|NLSPLINE}} = .TRUE.
			{{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:

Csheldon: /* Additional tags */

2025-03-31T08:06:51Z

Additional tags

← Older revision		Revision as of 08:06, 31 March 2025
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	Several additional {{FILE\|INCAR}} tags should be considered. Specifically, {{TAG\|LASPH}} should be set to <code>.TRUE.</code>, turning on the non-spherical contributions to the gradient of the density inside the PAW spheres. Occasionally, e.g. for systems containing H or first-row elements, and short bonds, the two-center contributions to the augmentation currents in the PAW spheres are important. In this case, {{TAG\|LLRAUG}} = .TRUE. should be used {{Cite\|dewijs:jcp:2013}}{{Cite\|dewijs:jcp:2021}}.		Several additional {{FILE\|INCAR}} tags should be considered. Specifically, {{TAG\|LASPH}} should be set to <code>.TRUE.</code>, turning on the non-spherical contributions to the gradient of the density inside the PAW spheres. Occasionally, e.g. for systems containing H or first-row elements, and short bonds, the two-center contributions to the augmentation currents in the PAW spheres are important. In this case, {{TAG\|LLRAUG}} = .TRUE. should be used {{Cite\|dewijs:jcp:2013}}{{Cite\|dewijs:jcp:2021}}.

	Calculating the chemical shift can also be sped up by utilizing parallelisation. If you are using multiple k-points, then you can treat these in parallel using {{TAG\|KPAR}}.		Calculating the chemical shift can also be sped up by utilizing parallelisation. If you are using multiple k-points, then you can treat these in parallel using {{TAG\|KPAR}}, reducing the overall calculation time.
	{{NB\|important\|The treatment of the orbital magnetism is non-relativistic. This is suitable for light nuclei.		{{NB\|important\|The treatment of the orbital magnetism is non-relativistic. This is suitable for light nuclei.
	The standard POTCARs are scalar-relativistic and account partially for relativistic effects.		The standard POTCARs are scalar-relativistic and account partially for relativistic effects.

Csheldon: /* Additional tags */

2025-03-31T08:04:38Z

Additional tags

← Older revision		Revision as of 08:04, 31 March 2025
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	Several additional {{FILE\|INCAR}} tags should be considered. Specifically, {{TAG\|LASPH}} should be set to <code>.TRUE.</code>, turning on the non-spherical contributions to the gradient of the density inside the PAW spheres. Occasionally, e.g. for systems containing H or first-row elements, and short bonds, the two-center contributions to the augmentation currents in the PAW spheres are important. In this case, {{TAG\|LLRAUG}} = .TRUE. should be used {{Cite\|dewijs:jcp:2013}}{{Cite\|dewijs:jcp:2021}}.		Several additional {{FILE\|INCAR}} tags should be considered. Specifically, {{TAG\|LASPH}} should be set to <code>.TRUE.</code>, turning on the non-spherical contributions to the gradient of the density inside the PAW spheres. Occasionally, e.g. for systems containing H or first-row elements, and short bonds, the two-center contributions to the augmentation currents in the PAW spheres are important. In this case, {{TAG\|LLRAUG}} = .TRUE. should be used {{Cite\|dewijs:jcp:2013}}{{Cite\|dewijs:jcp:2021}}.

			Calculating the chemical shift can also be sped up by utilizing parallelisation. If you are using multiple k-points, then you can treat these in parallel using {{TAG\|KPAR}}.
	{{NB\|important\|The treatment of the orbital magnetism is non-relativistic. This is suitable for light nuclei.		{{NB\|important\|The treatment of the orbital magnetism is non-relativistic. This is suitable for light nuclei.
	The standard POTCARs are scalar-relativistic and account partially for relativistic effects.		The standard POTCARs are scalar-relativistic and account partially for relativistic effects.

Csheldon: /* References */

2025-03-19T09:44:02Z

References

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

	[[Category:Howto]][[Category:NMR]][[Category:Linear response~~]][[Category:Chemical shifts~~]]		[[Category:Howto]][[Category:NMR]][[Category:Linear response]]

Csheldon at 09:43, 19 March 2025

2025-03-19T09:43:49Z

← Older revision		Revision as of 09:43, 19 March 2025
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	==References==		==References==

	~~<!--~~ [[Category:Howto]][[Category:NMR]][[Category:Linear response]][[Category:Chemical shifts]] ~~--!>~~		[[Category:Howto]][[Category:NMR]][[Category:Linear response]][[Category:Chemical shifts]]

Csheldon: Csheldon moved page Construction:NMR to Calculating the chemical shieldings

2025-03-10T09:31:05Z

Csheldon moved page Construction:NMR to Calculating the chemical shieldings

← Older revision		Revision as of 09:31, 10 March 2025
(No difference)

Csheldon: /* Energy cutoff tests */

2025-03-07T15:38:09Z

Energy cutoff tests

← Older revision		Revision as of 15:38, 7 March 2025
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	{{TAGBL\|NLSPLINE}} = .TRUE.		{{TAGBL\|NLSPLINE}} = .TRUE.

	Script to loop through {{TAG\|ENCUT}} from 400 eV to ~~600~~ eV:		Script to loop through {{TAG\|ENCUT}} from 400 eV to 800 eV:
	<pre>		<pre>
	for a in 400 500 600 700 800		for a in 400 500 600 700 800

Csheldon: /* Energetic break criterion tests */

2025-03-07T15:29:49Z

Energetic break criterion tests

← Older revision		Revision as of 15:29, 7 March 2025
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	'''INCAR.nmr'''		'''INCAR.nmr'''
	{{TAGBL\|PREC}} = Accurate		{{TAGBL\|PREC}} = Accurate
	{{TAGBL\|ENCUT}} = ~~600~~.0		{{TAGBL\|ENCUT}} = 400.0
	{{TAGBL\|EDIFF}} = 1E-8		{{TAGBL\|EDIFF}} = 1E-4
	{{TAGBL\|ISMEAR}} = 0; {{TAGBL\|SIGMA}} = 0.1		{{TAGBL\|ISMEAR}} = 0; {{TAGBL\|SIGMA}} = 0.1
	{{TAGBL\|LREAL}} = A		{{TAGBL\|LREAL}} = A

← Older revision		Revision as of 10:20, 16 March 2026
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	{{TAGBL\|ICHIBARE}} = 1		{{TAGBL\|ICHIBARE}} = 1
	{{TAGBL\|LNMR_SYM_RED}} = .TRUE.		{{TAGBL\|LNMR_SYM_RED}} = .TRUE.
	{{TAGBL\|NLSPLINE}} = .TRUE.		{{TAGBL\|NLSPLINE}} = .TRUE.
			{{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 15:29, 7 March 2025
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	'''INCAR.nmr'''		'''INCAR.nmr'''
	{{TAGBL\|PREC}} = Accurate		{{TAGBL\|PREC}} = Accurate
	{{TAGBL\|ENCUT}} = ~~600~~.0		{{TAGBL\|ENCUT}} = 400.0
	{{TAGBL\|EDIFF}} = 1E-8		{{TAGBL\|EDIFF}} = 1E-4
	{{TAGBL\|ISMEAR}} = 0; {{TAGBL\|SIGMA}} = 0.1		{{TAGBL\|ISMEAR}} = 0; {{TAGBL\|SIGMA}} = 0.1
	{{TAGBL\|LREAL}} = A		{{TAGBL\|LREAL}} = A