mirror of https://github.com/abinit/abinit.git
40 lines
1.8 KiB
Markdown
40 lines
1.8 KiB
Markdown
---
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description: How to calculate crossing barriers
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authors: GG
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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 calculate barriers for crossings with the ABINIT package,
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as well as ensemble DFT, or the pSIC approach to polaron formation.
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## Introduction
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The knowledge of geometries at which crossings between two electronic states happen,
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with minimal energy, or geometries at which the energy difference between the ground state and the excited
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state is small, and the energy is still low, plays an important role
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in the study of non-radiative transitions.
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It is possible to formulate the search for such geometries in terms of minimisation
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of a functional that is the linear combination of the energy of the two states at the same geometry,
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with Lagrange multipliers [[cite:Jia2019]].
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This is also related with a simple approach to Ensemble DFT: just make a linear combination of the DFT energies, the XC correlation
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energy being not computed with a single common density, but from each density separately.
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Also, the pSIC, polaron self-interaction corrected method [[cite:Sadigh2015]], [[cite:Sadigh2015a]], can be formulated in the same terms.
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In ABINIT, with [[imgmov]]==6, it is possible to deal with such
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linear combination of systems with the same geometry, but differing occupation factors [[occ]], and even
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with different [[cellcharge]]..
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It is possible to find the geometry at which the resulting energy is minimal, for a given value of the mixing factors [[mixesimgf]].
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Set [[nimage]]=2, and set the occupation numbers for image 1 to the ground-state occupations, and for image 2 to the excited-state occupations.
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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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## Tutorials
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