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![(Color online) (a) Spin and charge structure factors S(q) and C(q) at some relevant wave vectors. [The two S(q) for different momenta lie on top of each other.] (b) Charge gap c at different values of V and V = V /2 in the mean field and exact diagonalization.](profile/Jean-Paul-Pouget/publication/280576182/figure/fig3/AS:670710817099791@1536921328705/Color-online-a-Spin-and-charge-structure-factors-Sq-and-Cq-at-some-relevant-wave.png)
(Color online) (a) Spin and charge structure factors S(q) and C(q) at some relevant wave vectors. [The two S(q) for different momenta lie on top of each other.] (b) Charge gap c at different values of V and V = V /2 in the mean field and exact diagonalization.
Source publication
Combining density-functional theory and many-body approaches we investigate the origin of the ferroelectric
phase generally observed in TMTTF2-X organic crystals. We solve by means of mean-field theory and exact
diagonalization a two-dimensional tight-biding model built from density-functional theory calculations and we
show that short-range intera...
Contexts in source publication
Context 1
... Fig. 3 we show C(q) and S(q) for the momenta that maximize the response functions as a function of V . The exact C(q) confirms indeed that V favors CO with wave vector q = (π,0) (4k F ) for V 0.2 eV [see Fig. 3(a)], while for small V it is competitive with the q = (π,π) CO (not shown). . It is easy to realize that the combined charge and spin ...
Context 2
... Fig. 3 we show C(q) and S(q) for the momenta that maximize the response functions as a function of V . The exact C(q) confirms indeed that V favors CO with wave vector q = (π,0) (4k F ) for V 0.2 eV [see Fig. 3(a)], while for small V it is competitive with the q = (π,π) CO (not shown). . It is easy to realize that the combined charge and spin orderings reproduce phases 8 and 9 shown in Fig. 2. The effect of quantum fluctuations can be estimated by computing the reduction of the charge gap c with respect to the mean field. c is calculated by ...
Context 3
... to realize that the combined charge and spin orderings reproduce phases 8 and 9 shown in Fig. 2. The effect of quantum fluctuations can be estimated by computing the reduction of the charge gap c with respect to the mean field. c is calculated by averaging over twisted boundary conditions 24 in order to reduce finite-size effects and is shown in Fig. 3(b). c remains finite over the entire range of V and it only moderately decreases from the mean-field value, confirming the solidity of the present results. Increasing the lattice size is expected to reduce the value of the charge gap moving toward the experimental value, 25 suggesting that a moderate value of V may be relevant for such ...
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Citations
A material showing a spontaneous electric polarization that can be reversed by the application of an external electric field is said to be ferroelectric. Ferroelectricity is an important topic in condensed-matter physics with applications in memory devices. The Rochelle salt is the first ferroelectric crystal based on organic molecules, discovered in 1920. The lightness, flexibility and non-toxicity of organic ferroelectrics make them promising materials in the emerging field of organic electronics.
The purpose of the present chapter is to describe how computational crystallography combined with density functional theory calculations represent a useful tool for studying ferroelectricity in crystalline compounds. Our approach is based on the description of the main physical concepts, in an intuitive and qualitative way rather than using a formal mathematical approach. The outline is as follows: we will give an introduction to density functional theory and to modern theory of polarization; then we will proceed to a brief overview of group theory and the basic computational crystallography tools; finally we will discuss case studies such as organic ferroelectrics in order to provide a step-by-step procedure for the analysis of the ferroelectric polarization by using symmetry mode analysis.
