<div>Dear Stefano:</div>
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<div>Thank you very much for the answers. I lernt much from those. In some textbook the force constant matrix are </div>
<div> ( L L' )</div>
<div>F ( )<br> alpha,beta ( K K' ) L is the index of cells, K index of different atoms.</div>
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<div>(1) Can I rewrite the F_(alpha,beta)^(na,nb)(R) as</div>
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<div> ( 0 L' )</div>
<div>F ( ) while L' is L(a,b,c) L(R) ?<br> alpha,beta ( na nb ) </div></div>
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<div>(2) F_{alpha,beta} matrix is 3X3 matrix. And It acts like other two rank tensor ( dielectric tensor, electric conductivity tensor) under symmetry operations ? The independent parameters can be decided by group theory ? one for cubic system.</div>
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<div>(3) I pick up the </div>
<div>" x x 1 1</div>
<div> 2 1 1 x.xxxx " </div>
<div>lines</div>
<div>================</div>
<div> 1 1 1 1<br> 1 1 1 4.30811843056E-02<br> 2 1 1 1.49655475926E-02</div>
<div> 1 2 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 1 3 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 2 1 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 2 2 1 1<br> 1 1 1 4.30811843056E-02<br> 2 1 1 2.68996333333E-03</div>
<div> 2 3 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 3 1 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 3 2 1 1<br> 1 1 1 0.00000000000E+00<br> 2 1 1 0.00000000000E+00</div>
<div> 3 3 1 1<br> 1 1 1 4.30811843056E-02<br> 2 1 1 2.68996333333E-03</div>
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<div>why Fxx /= Fyy = Fzz ?</div>
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<div>I am sorry for my poor english. Also sorry for so many annoying question, self-teaching is a hard and careful work.</div>
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<div>Dr Zhou Bo</div>
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<div>Norhwest University Xi'an China</div>
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