# start Validation Reply Form
_vrf_PLAT971_I
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PROBLEM: Check Calcd Resid. Dens.  2.42A   From Pd1             4.19 eA-3  
RESPONSE: The high peak of residual electron density have distances to the nearest Pd atom suibtable 
for a Pd-As bond. But the value of the peak is too small to be fully occupated by Pd or As.
 Several model were treated to resolved the problem. 
1. The peak was treated as additional position of As atoms with very small partial occupation. 
2. The disorder of As3 atoms over two position was treated. In both cases refinement was unstable.
3. The twinning models were tested too. They were led to very high R-factors.
On the other hand, the SEM analysis of the crystal gave composition Pd8As3 with average variation 0.05 a.p.f.u. 
The model, received from our structure refinement, gave the same strutural formula. 
If we add any portion of Pd or As atoms, the balance is break.  
That means that the model with vacation at the position "0 0 1/2" is the most reasonable. 
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# end Validation Reply Form