mirror of https://github.com/abinit/abinit.git
36 lines
1.3 KiB
Markdown
36 lines
1.3 KiB
Markdown
---
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description: How to perform a Δ-SCF calculation of neutral excitations
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authors: FJ
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---
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<!--- This is the source file for this topics. Can be edited. -->
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This page gives hints on how to perform a Δ-SCF calculation of neutral excitations with the ABINIT package.
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## Introduction
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Although formally not justified, difference in total energy using constrained
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occupation numbers sometimes results in surprisingly good agreement with
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experimental results, for neutral excitations, in molecules or doped solids.
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See e.g. [[cite:Jia2017]].
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The manual specification of the occupation numbers is needed in this case.
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This is accomplished with the input variable [[occ]], coupled with
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[[occopt]]=0 for the homogeneous occupation of a band throughout the Brillouin
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Zone, or with [[occopt]]=2 for the specific occupation of a state for a
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selected k-wavevector. For very big cells, both should be equivalent, and
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[[occopt]]=0 is easier to use.
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The "linear combination of images" algorithm allows one to work with a set
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of images of the same geometry, but with different electronic states,
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and even to optimize this geometry,
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according to the linear combination of forces, see [[imgmov]]=6 and [[mixesimgf]].
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## Related Input Variables
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{{ related_variables }}
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## Selected Input Files
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{{ selected_input_files }}
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