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["张�s" <zhangting1980323@gmail.com>]

Dear All:

    I'm calculating the elph matrix with ABINIT code. I find that the calculated elph matrix elements change their sign via k-point, and I feel this quite strange. For example, I'm calculating a testing system which is a carbon atom chain. The system has two carbon atoms in an unit cell, 8 bands, and the fermi level is located between iband = 4 and iband =5. I expect the elph coupling between these two bands near fermi k-point(k = -0.5 , k=0.5) is  important. So with phonon's q =0, I calculated the elph matrix g(k,k+q,ib1,ib2). The results seems strange because the elph matrix element change their sign via k-point, see below:

q =0, branch =6 (the LO mode, which should be the strongest el-ph coupling mode in C2 chain)
ib1=4,ib2=5,
k=-0.475, gkk(pert=atom1, z-direction)=-2.432264e-002 +i*8.642045e-001, gkk(pert=atom2,z-direction)=2.432269e-002 +i*-8.642045e-001
k=-0.425, gkk(pert=atom1, z-direction)=2.397082e-002 +i*-8.564656e-001, gkk(pert=atom2,z-direction)=-2.397087e-002 +i*8.564656e-001
k=-0.375, gkk(pert=atom1, z-direction)=-2.323420e-002 +i*8.402542e-001, gkk(pert=atom2,z-direction)=2.323425e-002 +i*-8.402542e-001
k=-0.325, gkk(pert=atom1, z-direction)=-2.204158e-002 +i*8.139450e-001, gkk(pert=atom2,z-direction)=2.204164e-002 +i*-8.139450e-001
k=-0.275, gkk(pert=atom1, z-direction)=2.027373e-002 +i*-7.746554e-001, gkk(pert=atom2,z-direction)=-2.027378e-002 +i*7.746554e-001 
We can see that from k= -0.475 --> k= -0.425, the gkk change sign. Also I can not find any rule in the sign change. Why these gkk element change sign via k-points? And is this result correct? Thanks! My input file is attached.  


Regards


                                                        Zhang Ting
                                                        Peking Univ.
                                                        Jun, 29th. 2008

Attachment: C2.in
Description: Binary data