Update publications

content/publication/selenius-2024/cite.bib

@@ -1,5 +1,5 @@
 @article{Selenius2024,
- abstract = {A strategy is presented for variational orbital optimization in time-independent calculations of excited electronic states. The approach involves minimizing the energy while constraining the degrees of freedom corresponding to negative curvature on the electronic energy surface, followed by fully unconstrained optimization, thereby converging on a saddle point. Both steps of this freeze-and-release strategy are carried out via direct orbital optimization at a similar cost as ground state calculations. The approach is applied in orbital optimized density functional calculations and is shown to converge intramolecular charge transfer excited states where the common maximum overlap method is unable to prevent collapse to unphysical, charge-delocalized solutions. The constrained minimization can also be used to improve the estimate of the saddle point order of the target excited state solution, which is required as input for generalized mode following methods. Calculations with the local density approximation and the generalized gradient approximation functionals PBE and BLYP are carried out for a large set of charge transfer excitations in organic molecules using both direct optimization as well as the linear-response time-dependent density functional theory (TD-DFT) method. The time-independent approach is fully variational and provides a relaxed excited state electron density that can be used to quantify the extent of charge transfer. The TD-DFT calculations are found to generally overestimate the charge transfer distance compared to the orbital optimized calculations, even when the TD-DFT relaxed density is used. Furthermore, the orbital optimized calculations yield more accurate excitation energy values relative to the theoretical best estimates for the medium and long-range charge transfer distances, where the errors of TD-DFT are as large as 2 eV.},
+ abstract = {The performance of time-independent, orbital optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital optimized calculations, even when including first-order orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. −2 eV for TD-DFT, no correlation is observed for the orbital optimized approach. The orbital optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with long-range charge transfer character. Orbital optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.},
  archiveprefix = {arXiv},
  arxivid = {2311.01604},
  author = {Selenius, Elli and Sigurðarson, Alec Elías and Schmerwitz, Yorick L. A. and Levi, Gianluca},

content/publication/selenius-2024/index.md

@@ -12,29 +12,7 @@ publication_types:
 - article-journal
 publication: '*Journal of Chemical Theory and Computation (accepted)*'
 doi: 10.48550/arXiv.2311.01604
-abstract: A strategy is presented for variational orbital optimization in time-independent
-  calculations of excited electronic states. The approach involves minimizing the
-  energy while constraining the degrees of freedom corresponding to negative curvature
-  on the electronic energy surface, followed by fully unconstrained optimization,
-  thereby converging on a saddle point. Both steps of this freeze-and-release strategy
-  are carried out via direct orbital optimization at a similar cost as ground state
-  calculations. The approach is applied in orbital optimized density functional calculations
-  and is shown to converge intramolecular charge transfer excited states where the
-  common maximum overlap method is unable to prevent collapse to unphysical, charge-delocalized
-  solutions. The constrained minimization can also be used to improve the estimate
-  of the saddle point order of the target excited state solution, which is required
-  as input for generalized mode following methods. Calculations with the local density
-  approximation and the generalized gradient approximation functionals PBE and BLYP
-  are carried out for a large set of charge transfer excitations in organic molecules
-  using both direct optimization as well as the linear-response time-dependent density
-  functional theory (TD-DFT) method. The time-independent approach is fully variational
-  and provides a relaxed excited state electron density that can be used to quantify
-  the extent of charge transfer. The TD-DFT calculations are found to generally overestimate
-  the charge transfer distance compared to the orbital optimized calculations, even
-  when the TD-DFT relaxed density is used. Furthermore, the orbital optimized calculations
-  yield more accurate excitation energy values relative to the theoretical best estimates
-  for the medium and long-range charge transfer distances, where the errors of TD-DFT
-  are as large as 2 eV.
+abstract: The performance of time-independent, orbital optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital optimized calculations, even when including first-order orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. −2 eV for TD-DFT, no correlation is observed for the orbital optimized approach. The orbital optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with long-range charge transfer character. Orbital optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.
 links:
 - name: arXiv
   url: https://arxiv.org/abs/2311.01604

public/publication-type/article-journal/index.html

@@ -905,7 +905,7 @@ <h1>article-journal</h1>
 
     <a href="/publication/selenius-2024/"  class="summary-link">
       <div class="article-style">
-        A strategy is presented for variational orbital optimization in time-independent calculations of excited electronic states. The …
+        The performance of time-independent, orbital optimized calculations of excited states is assessed with respect to charge transfer …
       </div>
     </a>
 

public/publication/selenius-2024/cite.bib

@@ -1,5 +1,5 @@
 @article{Selenius2024,
- abstract = {A strategy is presented for variational orbital optimization in time-independent calculations of excited electronic states. The approach involves minimizing the energy while constraining the degrees of freedom corresponding to negative curvature on the electronic energy surface, followed by fully unconstrained optimization, thereby converging on a saddle point. Both steps of this freeze-and-release strategy are carried out via direct orbital optimization at a similar cost as ground state calculations. The approach is applied in orbital optimized density functional calculations and is shown to converge intramolecular charge transfer excited states where the common maximum overlap method is unable to prevent collapse to unphysical, charge-delocalized solutions. The constrained minimization can also be used to improve the estimate of the saddle point order of the target excited state solution, which is required as input for generalized mode following methods. Calculations with the local density approximation and the generalized gradient approximation functionals PBE and BLYP are carried out for a large set of charge transfer excitations in organic molecules using both direct optimization as well as the linear-response time-dependent density functional theory (TD-DFT) method. The time-independent approach is fully variational and provides a relaxed excited state electron density that can be used to quantify the extent of charge transfer. The TD-DFT calculations are found to generally overestimate the charge transfer distance compared to the orbital optimized calculations, even when the TD-DFT relaxed density is used. Furthermore, the orbital optimized calculations yield more accurate excitation energy values relative to the theoretical best estimates for the medium and long-range charge transfer distances, where the errors of TD-DFT are as large as 2 eV.},
+ abstract = {The performance of time-independent, orbital optimized calculations of excited states is assessed with respect to charge transfer excitations in organic molecules in comparison to the linear-response time-dependent density functional theory (TD-DFT) approach. A direct optimization method to converge on saddle points of the electronic energy surface is used to carry out calculations with the local density approximation (LDA) and the generalized gradient approximation (GGA) functionals PBE and BLYP for a set of 27 excitations in 15 molecules. The time-independent approach is fully variational and provides a relaxed excited state electron density from which the extent of charge transfer is quantified. The TD-DFT calculations are generally found to provide larger charge transfer distances compared to the orbital optimized calculations, even when including first-order orbital relaxation effects with the Z-vector method. While the error on the excitation energy relative to theoretical best estimates is found to increase with the extent of charge transfer up to ca. −2 eV for TD-DFT, no correlation is observed for the orbital optimized approach. The orbital optimized calculations with the LDA and the GGA functionals provide a mean absolute error of ∼0.7 eV, outperforming TD-DFT with both local and global hybrid functionals for excitations with long-range charge transfer character. Orbital optimized calculations with the global hybrid functional B3LYP and the range-separated hybrid functional CAM-B3LYP on a selection of states with short- and long-range charge transfer indicate that inclusion of exact exchange has a small effect on the charge transfer distance, while it significantly improves the excitation energy, with the best performing functional CAM-B3LYP providing an absolute error typically around 0.15 eV.},
  archiveprefix = {arXiv},
  arxivid = {2311.01604},
  author = {Selenius, Elli and Sigurðarson, Alec Elías and Schmerwitz, Yorick L. A. and Levi, Gianluca},