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7.22 I do not get the same results in different machines!

If the difference is small, do not panic. It is quite normal for iterative methods to reach convergence through different paths as soon as anything changes. In particular, between serial and parallel execution there are operations that are not performed in the same order. As the numerical accuracy of computer numbers is finite, this can yield slightly different results.

It is also normal that the total energy converges to a better accuracy than its terms, since only the sum is variational, i.e. has a minimum in correspondence to ground-state charge density. Thus if the convergence threshold is for instance 10-8 , you get 8-digit accuracy on the total energy, but one or two less on other terms (e.g. XC and Hartree energy). It this is a problem for you, reduce the convergence threshold for instance to 10-10 or 10-12 . The differences should go away (but it will probably take a few more iterations to converge).


next up previous contents
Next: 7.23 the CPU time Up: 7 Troubleshooting Previous: 7.21 warning: 'symmetry operation Contents
Paolo Giannozzi 2009-10-01