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'''Racah's W-coefficients''' were introduced by [[Giulio Racah]] in 1942.<ref>{{Cite journal |first=G. |last=Racah |title=Theory of Complex Spectra II |journal=[[Physical Review]] |volume=62 |issue=9–10 |pages=438–462 |year=1942 |doi=10.1103/PhysRev.62.438 |bibcode = 1942PhRv...62..438R }}</ref> These coefficients have a purely mathematical definition. In physics they are used in calculations involving the [[quantum mechanics|quantum mechanical]] description of [[angular momentum]], for example in [[atomic theory]]. | |||
The coefficients appear when there are three sources of angular momentum in the problem. For example, consider an atom with one electron in an [[atomic orbital|s orbital]] and one electron in a [[atomic orbital|p orbital]]. Each electron has [[electron spin]] angular momentum and in addition | |||
the p orbital has orbital angular momentum (an s orbital has zero orbital angular momentum). The atom may be described by ''LS'' coupling or by ''jj'' coupling as explained in the article on [[angular momentum coupling]]. The transformation between the wave functions that correspond to these two couplings involves a Racah W-coefficient. | |||
Apart from a phase factor, Racah's W-coefficients are equal to Wigner's [[6-j symbol]]s, so any equation involving Racah's W-coefficients may be rewritten using 6-j symbols. This is often advantageous because the symmetry properties of 6-j symbols are easier to remember. | |||
Racah coefficients are related to recoupling coefficients by | |||
:<math> | |||
W(j_1j_2Jj_3;J_{12}J_{23}) \equiv [(2J_{12}+1)(2J_{23}+1)]^{-\frac{1}{2}} | |||
\langle (j_1, (j_2j_3)J_{23}) J | ((j_1j_2)J_{12},j_3)J \rangle. | |||
</math> | |||
Recoupling coefficients are elements of a [[unitary transformation]] and their definition is given in the next section. Racah coefficients have more convenient symmetry properties than the recoupling coefficients (but less convenient than the 6-j symbols). | |||
==Recoupling coefficients== | |||
Coupling of two angular momenta <math>\mathbf{j}_1</math> and <math>\mathbf{j}_2</math> is the construction of simultaneous eigenfunctions of <math>\mathbf{J}^2</math> and <math>J_z</math>, where <math>\mathbf{J}=\mathbf{j}_1+\mathbf{j}_2</math>, as explained in the article on [[Clebsch-Gordan coefficients]]. The result is | |||
:<math> | |||
|(j_1j_2)JM\rangle = \sum_{m_1=-j_1}^{j_1} \sum_{m_2=-j_2}^{j_2} | |||
|j_1m_1\rangle |j_2m_2\rangle \langle j_1m_1j_2m_2|JM\rangle, | |||
</math> | |||
where <math>J=|j_1-j_2|,\ldots,j_1+j_2</math> and <math>M=-J,\ldots,J</math>. | |||
Coupling of three angular momenta <math>\mathbf{j}_1</math>, <math>\mathbf{j}_2</math>, and <math>\mathbf{j}_3</math>, may be done by first coupling <math>\mathbf{j}_1</math> and <math>\mathbf{j}_2</math> to <math>\mathbf{J}_{12}</math> and next coupling <math>\mathbf{J}_{12}</math> and <math>\mathbf{j}_3</math> to total angular momentum <math>\mathbf{J}</math>: | |||
:<math> | |||
|((j_1j_2)J_{12}j_3)JM\rangle = \sum_{M_{12}=-J_{12}}^{J_{12}} \sum_{m_3=-j_3}^{j_3} | |||
|(j_1j_2)J_{12}M_{12}\rangle |j_3m_3\rangle \langle J_{12}M_{12}j_3m_3|JM\rangle | |||
</math> | |||
Alternatively, one may first couple <math>\mathbf{j}_2</math> and <math>\mathbf{j}_3</math> to <math>\mathbf{J}_{23}</math> and next couple <math>\mathbf{j}_1</math> and <math>\mathbf{J}_{23}</math> to <math>\mathbf{J}</math>: | |||
:<math> | |||
|(j_1,(j_2j_3)J_{23})JM \rangle = \sum_{m_1=-j_1}^{j_1} \sum_{M_{23}=-J_{23}}^{J_{23}} | |||
|j_1m_1\rangle |(j_2j_3)J_{23}M_{23}\rangle \langle j_1m_1J_{23}M_{23}|JM\rangle | |||
</math> | |||
Both coupling schemes result in complete orthonormal bases for the <math>(2j_1+1)(2j_2+1)(2j_3+1)</math> dimensional space spanned by | |||
:<math> | |||
|j_1 m_1\rangle |j_2 m_2\rangle |j_3 m_3\rangle, \;\; m_1=-j_1,\ldots,j_1;\;\; m_2=-j_2,\ldots,j_2;\;\; m_3=-j_3,\ldots,j_3. | |||
</math> | |||
Hence, the two total angular momentum bases are related by a unitary transformation. The matrix elements of this unitary transformation are given by a [[scalar product]] and are known as recoupling coefficients. The coefficients are independent of <math>M</math> and so we have | |||
:<math> | |||
|((j_1j_2)J_{12}j_3)JM\rangle = \sum_{J_{23}} |(j_1,(j_2j_3)J_{23})JM \rangle | |||
\langle (j_1,(j_2j_3)J_{23})J |((j_1j_2)J_{12}j_3)J\rangle. | |||
</math> | |||
The independence of <math>M</math> follows readily by writing this equation for <math>M=J</math> and applying the [[Clebsch-Gordan coefficient#Angular momentum operators|lowering operator]] <math>J_-</math> to both sides of the equation. | |||
==Algebra== | |||
Let | |||
:<math>\Delta(a,b,c)=[(a+b-c)!(a-b+c)!(-a+b+c)!/(a+b+c+1)!]^{1/2}</math> | |||
be the usual triangular factor, then the Racah coefficient is a product | |||
of four of these by a sum over factorials, | |||
:<math>W(abcd;ef)=\Delta(a,b,e)\Delta(c,d,e)\Delta(a,c,f)\Delta(b,d,f)w(abcd;ef) | |||
</math> | |||
where | |||
:<math>w(abcd;ef)\equiv | |||
\sum_z\frac{(-1)^{z+\beta_1}(z+1)!}{(z-\alpha_1)!(z-\alpha_2)!(z-\alpha_3)! | |||
(z-\alpha_4)!(\beta_1-z)!(\beta_2-z)!(\beta_3-z)!}</math> | |||
and | |||
:<math>\alpha_1=a+b+e;\quad \beta_1=a+b+c+d;</math> | |||
:<math>\alpha_2=c+d+e;\quad \beta_2=a+d+e+f;</math> | |||
:<math>\alpha_3=a+c+f;\quad \beta_3=b+c+e+f;</math> | |||
:<math>\alpha_4=b+d+f.</math> | |||
The sum over <math>z</math> is finite over the range<ref>The Theory of Atomic Structure and Spectra, Cowan, p. 148</ref> | |||
:<math> \max(\alpha_1,\alpha_2,\alpha_3,\alpha_4) \le z \le \min(\beta_1,\beta_2,\beta_3). </math> | |||
==Relation to Wigner's 6-j symbol== | |||
Racah's W-coefficients are related to Wigner's [[6-j symbol]]s, which have even more convenient symmetry properties | |||
:<math> | |||
W(abcd;ef)(-1)^{a+b+c+d}= | |||
\begin{Bmatrix} | |||
a&b&e\\ | |||
d&c&f | |||
\end{Bmatrix}. | |||
</math> | |||
See <ref>Angular momentum 3<math>^{rd}</math> ed. by D.M. Brink and G.R. Satchler Page 142 </ref> or | |||
:<math> | |||
W(j_1j_2Jj_3;J_{12}J_{23}) = (-1)^{j_1+j_2+j_3+J} | |||
\begin{Bmatrix} | |||
j_1 & j_2 & J_{12}\\ | |||
j_3 & J & J_{23} | |||
\end{Bmatrix}. | |||
</math> | |||
==See also== | |||
* [[Clebsch–Gordan coefficients]] | |||
* [[3-jm symbol]] | |||
* [[6-j symbol]] | |||
==Notes== | |||
{{Reflist}} | |||
==Further reading== | |||
* {{cite book |last= Edmonds |first= A. R. |title= Angular Momentum in Quantum Mechanics |year= 1957 | |||
|publisher= [[Princeton University Press]] |location= Princeton, New Jersey |isbn= 0-691-07912-9}} | |||
* {{cite book |last= Condon |first= Edward U. |coauthors= Shortley, G. H. |title= The Theory of Atomic Spectra |year= 1970 | |||
|publisher= [[Cambridge University Press]] |location= Cambridge |isbn= 0-521-09209-4 |chapter= Chapter 3}} | |||
* {{cite book |last= Messiah |first= Albert |title= Quantum Mechanics (Volume II) |year= 1981 | edition= 12th edition | |||
|publisher= [[Elsevier|North Holland Publishing]] |location= New York |isbn= 0-7204-0045-7}} | |||
*{{cite journal | |||
|first=Masachiyo | |||
|last1=Sato | |||
|journal=Progr. Theor. Physics | |||
|volume=13 | |||
|issue=4 | |||
|year=1955 | |||
|pages=405–414 | |||
|title=General formula of the Racah coefficient | |||
|doi=10.1143/PTP.13.405 | |||
|bibcode=1955PThPh..13..405S | |||
}} | |||
* {{cite book |last= Brink |first= D. M. |coauthors= Satchler, G. R. |title= Angular Momentum | |||
|year= 1993 |edition= 3rd edition |publisher= [[Clarendon Press]] |location= Oxford |isbn= 0-19-851759-9 |chapter= Chapter 2 }} | |||
* {{cite book |last= Zare |first= Richard N. |title= Angular Momentum |year=1988 | |||
|publisher= [[John Wiley & Sons|John Wiley]] |location= New York |isbn= 0-471-85892-7 |chapter= Chapter 2}} | |||
* {{cite book |last= Biedenharn |first= L. C. |coauthors= Louck, J. D. |title= Angular Momentum in Quantum Physics | |||
|year= 1981 |publisher= [[Addison-Wesley]] |location= Reading, Massachusetts |isbn= 0-201-13507-8 }} | |||
==External links== | |||
* {{springer|title=Racah-Wigner coefficients|id=p/r110010}} | |||
[[Category:Rotational symmetry]] | |||
[[Category:Representation theory of Lie groups]] |
Revision as of 14:41, 20 April 2013
Racah's W-coefficients were introduced by Giulio Racah in 1942.[1] These coefficients have a purely mathematical definition. In physics they are used in calculations involving the quantum mechanical description of angular momentum, for example in atomic theory.
The coefficients appear when there are three sources of angular momentum in the problem. For example, consider an atom with one electron in an s orbital and one electron in a p orbital. Each electron has electron spin angular momentum and in addition the p orbital has orbital angular momentum (an s orbital has zero orbital angular momentum). The atom may be described by LS coupling or by jj coupling as explained in the article on angular momentum coupling. The transformation between the wave functions that correspond to these two couplings involves a Racah W-coefficient.
Apart from a phase factor, Racah's W-coefficients are equal to Wigner's 6-j symbols, so any equation involving Racah's W-coefficients may be rewritten using 6-j symbols. This is often advantageous because the symmetry properties of 6-j symbols are easier to remember.
Racah coefficients are related to recoupling coefficients by
Recoupling coefficients are elements of a unitary transformation and their definition is given in the next section. Racah coefficients have more convenient symmetry properties than the recoupling coefficients (but less convenient than the 6-j symbols).
Recoupling coefficients
Coupling of two angular momenta and is the construction of simultaneous eigenfunctions of and , where , as explained in the article on Clebsch-Gordan coefficients. The result is
Coupling of three angular momenta , , and , may be done by first coupling and to and next coupling and to total angular momentum :
Alternatively, one may first couple and to and next couple and to :
Both coupling schemes result in complete orthonormal bases for the dimensional space spanned by
Hence, the two total angular momentum bases are related by a unitary transformation. The matrix elements of this unitary transformation are given by a scalar product and are known as recoupling coefficients. The coefficients are independent of and so we have
The independence of follows readily by writing this equation for and applying the lowering operator to both sides of the equation.
Algebra
Let
be the usual triangular factor, then the Racah coefficient is a product of four of these by a sum over factorials,
where
and
The sum over is finite over the range[2]
Relation to Wigner's 6-j symbol
Racah's W-coefficients are related to Wigner's 6-j symbols, which have even more convenient symmetry properties
See [3] or
See also
Notes
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Further reading
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In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ The Theory of Atomic Structure and Spectra, Cowan, p. 148
- ↑ Angular momentum 3 ed. by D.M. Brink and G.R. Satchler Page 142