Electronic Structure of Some Model Anticancer Molecular Systems

2006 ◽  
pp. 1360-1363
Author(s):  
H Chojnacki
Keyword(s):  
Electronic Structure ◽  
Molecular Systems

scholarly journals Quantum HF/DFT-embedding algorithms for electronic structure calculations: Scaling up to complex molecular systems

2021 ◽  
Vol 154 (11) ◽  
pp. 114105
Author(s):  
Max Rossmannek ◽  
Panagiotis Kl. Barkoutsos ◽  
Pauline J. Ollitrault ◽  
Ivano Tavernelli
Keyword(s):  
Electronic Structure ◽  
Electronic Structure Calculations ◽  
Scaling Up ◽  
Molecular Systems ◽  
Structure Calculations

scholarly journals Accuracy and Reliability in the Simulation of Vibrational Spectra: A Comprehensive Benchmark of Energies and Intensities Issuing From Generalized Vibrational Perturbation Theory to Second Order (GVPT2)

2021 ◽  
Vol 8 ◽  
Author(s):  
Qin Yang ◽  
Marco Mendolicchio ◽  
Vincenzo Barone ◽  
Julien Bloino
Keyword(s):  
Perturbation Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Computational Cost ◽  
Theoretical Data ◽  
Infrared Region ◽  
Second Order ◽  
Basis Set ◽  
Molecular Systems ◽  
The Impact

Vibrational spectroscopy represents an active frontier for the identification and characterization of molecular species in the context of astrochemistry and astrobiology. As new missions will provide more data over broader ranges and at higher resolution, especially in the infrared region, which could be complemented with new spectrometers in the future, support from laboratory experiments and theory is crucial. In particular, computational spectroscopy is playing an increasing role in deepening our understanding of the origin and nature of the observed bands in extreme conditions characterizing the interstellar medium or some planetary atmospheres, not easily reproducible on Earth. In this connection, the best compromise between reliability, feasibility and ease of interpretation is still a matter of concern due to the interplay of several factors in determining the final spectral outcome, with larger molecular systems and non-covalent complexes further exacerbating the dichotomy between accuracy and computational cost. In this context, second-order vibrational perturbation theory (VPT2) together with density functional theory (DFT) has become particularly appealing. The well-known problem of the reliability of exchange-correlation functionals, coupled with the treatment of resonances in VPT2, represents a challenge for the determination of standardized or “black-box” protocols, despite successful examples in the literature. With the aim of getting a clear picture of the achievable accuracy and reliability of DFT-based VPT2 calculations, a multi-step study will be carried out here. Beyond the definition of the functional, the impact of the basis set and the influence of the resonance treatment in VPT2 will be analyzed. For a better understanding of the computational aspects and the results, a short summary of vibrational perturbation theory and the overall treatment of resonances for both energies and intensities will be given. The first part of the benchmark will focus on small molecules, for which very accurate experimental and theoretical data are available, to investigate electronic structure calculation methods. Beyond the reliability of energies, widely used for such systems, the issue of intensities will also be investigated in detail. The best performing electronic structure methods will then be used to treat larger molecular systems, with more complex topologies and resonance patterns.

scholarly journals Temperature and H/D Isotopic Effects in the IR Spectra of the Hydrogen Bond in Solid-State 2-Furanacetic Acid and 2-Furanacrylic Acid

2012 ◽  
Vol 2012 ◽  
pp. 1-17 ◽  
Author(s):  
Henryk T. Flakus ◽  
Anna Jarczyk-Jędryka
Keyword(s):  
Hydrogen Bond ◽  
Electronic Structure ◽  
Ir Spectra ◽  
Close Relation ◽  
Coupling Mechanism ◽  
Band Frequency ◽  
Molecular Systems ◽  
Exciton Coupling ◽  
Relative Contribution ◽  
Type Coupling

Polarized IR spectra of 2-furanacetic acid and of 2-furanacrylic acid crystals were measured at 293 K and 77 K in the vO−H and vO−H band frequency ranges. The corresponding spectra of the two individual systems strongly differ, one from the other, by the corresponding band shapes as well as by the temperature effect characterizing the bands. The crystal spectral properties remain in a close relation with the electronic structure of the two different molecular systems. We show that a vibronic coupling mechanism involving the hydrogen bond protons and the electrons on the π-electronic systems in the molecules determines the way in which the vibrational exciton coupling between the hydrogen bonds in the carboxylic acid dimers occurs. A strong coupling in 2-furanacrylic acid dimers prefers a “tail-to-head-” type Davydov coupling widespread by the π-electrons. A weak through-space coupling in 2-furanacetic acid dimers is responsible for a “side-to-side-” type coupling. The relative contribution of each exciton coupling mechanism in the dimer spectra generation is temperature and the molecular electronic structure dependent. This explains the observed difference in the temperature-induced evolution of the compared spectra.

scholarly journals Fast electronic structure methods for strongly correlated molecular systems

2005 ◽  
Vol 16 ◽  
pp. 233-242 ◽  
Author(s):  
Martin Head-Gordon ◽  
Gregory J O Beran ◽  
Alex Sodt ◽  
Yousung Jung
Keyword(s):  
Electronic Structure ◽  
Strongly Correlated ◽  
Molecular Systems ◽  
Electronic Structure Methods ◽  
Fast Electronic

The Electron Pair in Chemistry

1974 ◽  
Vol 52 (8) ◽  
pp. 1310-1320 ◽  
Author(s):  
R. Daudel ◽  
R. F. W. Bader ◽  
M. E. Stephens ◽  
D. S. Borrett
Keyword(s):  
Information Theory ◽  
Electronic Structure ◽  
Electron Pair ◽  
Real Space ◽  
Maximum Amount ◽  
Fundamental Unit ◽  
Electron Pairs ◽  
Molecular Systems ◽  
Amount Of Information ◽  
The One

The reality of the electron pair as a fundamental unit in the electronic structure of molecular systems is evidenced by calculations which show that the most probable partitioning of a system is the one which localizes pairs of electrons in well-defined spatial regions or loges. The loges in turn, correspond to those regions of space generally associated with core, bonded, and non-bonded electrons. In terms of information theory, they yield the maximum amount of information concerning the localizability of the electrons. The most probable three-loge partitioning of the six-electron BH(X1∑+) system, for example, is dominated by the event which places two electrons in each of three loges, the location and shape of the loges being such as to justify the labelling of the electron pairs they localize as core, bonded and nonbonded. Since the loges are defined in real space and are totally nonoverlapping, one may define the volume of space occupied by pairs of electrons. In BH, for example, the volume of space required to contain 95% of the nonbonded pair of electrons is over two times larger than that required to contain 95% of the bonded pair. It is possible to define core loges which exhibit pair occupation probabilities ranging in value from 95% in LiH+ to 85% in BH. Corresponding probabilities ranging in value from 75% to 90% are obtained for bonded and nonbonded loges. In the set of molecules studied here, the occurrence of events with such high probabilities is found only for loges which maximize the probability of a pair occupation.

scholarly journals Relativistic Fock Space Coupled Cluster Method for Many-Electron Systems: Non-Perturbative Account for Connected Triple Excitations

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1101 ◽  
Author(s):  
Alexander V. Oleynichenko ◽  
Andréi Zaitsevskii ◽  
Leonid V. Skripnikov ◽  
Ephraim Eliav
Keyword(s):  
Electronic Structure ◽  
Fock Space ◽  
Cluster Method ◽  
Coupled Cluster ◽  
Heavy Nuclei ◽  
Coupled Cluster Method ◽  
Molecular Systems ◽  
Cluster Operator ◽  
Zero Shift ◽  
Firm Basis

The Fock space relativistic coupled cluster method (FS-RCC) is one of the most promising tools of electronic structure modeling for atomic and molecular systems containing heavy nuclei. Until recently, capabilities of the FS-RCC method were severely restricted by the fact that only single and double excitations in the exponential parametrization of the wave operator were considered. We report the design and the first computer implementation of FS-RCC schemes with full and simplified non-perturbative account for triple excitations in the cluster operator. Numerical stability of the new computational scheme and thus its applicability to a wide variety of molecular electronic states is ensured using the dynamic shift technique combined with the extrapolation to zero-shift limit. Pilot applications to atomic (Tl, Pb) and molecular (TlH) systems reported in the paper indicate that the breakthrough in accuracy and predictive power of the electronic structure calculations for heavy-element compounds can be achieved. Moreover, the described approach can provide a firm basis for high-precision modeling of heavy molecular systems with several open shells, including actinide compounds.

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