Non-zero acoustic frequencies in Gamma point

Yaroslav · Post by **Yaroslav** » Tue Aug 26, 2014 12:49 am

Hello all,

I successfully finished the response function (RF1) calculation (analogue to trf1_5.in) of CsH2PO4 crystal (P2_1 sp. gr., Z=2), namely the computation of the response to homogeneous electric field and atomic displacements at q=0. The phonon mode frequencies are quite reasonable and manifest a reasonable LO-TO splitting. The problem is three non-zero acoustic frequencies, namely -2, -1, 2 cm^-1. I tried to use the Anaddb utility to correct these frequencies. Unfortunately, without a success. There are two DDB files, cdp_rf1o_DS1_DDB(1st derivatives) and cdp_rf1o_DS3_DDB (2nd derivatives), in output set of RF1 calculation. I used file cdp_rf1o_DS3_DDB for Anaddb utility. Unfortunately, I failed to get the correct result. I don't know why the Anaddb wants to calculate the dynamical matrices in all 64 points of Brillouin Zone. I need to correct only Gamma point dynamical matrix. Where is my fault?

I have got the following error
----------------------------------------------------------------------------
Calculation of the interatomic forces
-begin at tcpu 0.041 and twall 67.580 sec
before mkifc9
Simple Lattice Grid
symdm9 : the bloks found in the DDB are characterized
by the following wavevectors :
0.000000000000D+00 0.000000000000D+00 0.000000000000D+00 0.100000000000D+01

symdm9.F90:213:ERROR
Informations are missing in the DDB.
The dynamical matrix number 1 cannot be built,
since no blok with wavevector 1.250000E-01 1.250000E-01 1.250000E-01
has been found.
Action : add the required blok in the DDB, or modify your input file.

leave_new : decision taken to exit ...
---------------------------------------------------------------------------------------------------------------
My question is: Must I calculate the dynamical matrices in all 64 points of BZ?

I would be grateful for any hint,

Best regards,
Yaroslav