Differences

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--- limitations [2013/02/28 13:31] – created daniel
+++ limitations [2018/01/05 10:48] (current) – daniel
@@ Line 1: / Line 1: @@
-__NOTOC__
+~~NOTOC~~
+====== Limitations ======
+----
 Limitations of the current implemetation:
 ===== Spline Interpolation =====
-At the moment, ''potfit'' takes its tabulated potential functions through values at sampling points and spline interpolation in between. While this allows considerable flexibility, it also has some disadvantages. Especially for distance ranges with rapid changes in function values, the spline polynomials might produce overswings. Users need to keep an eye on the interpolated functions to check if they suffer from potential artefacts.
+At the moment, //potfit// takes its tabulated potential functions through values at sampling points and spline interpolation in between. While this allows considerable flexibility, it also has some disadvantages. Especially for distance ranges with rapid changes in function values, the spline polynomials might produce overswings. Users need to keep an eye on the interpolated functions to check if they suffer from potential artefacts.
-For analytic potentials this is not a problem, because the functions are sampled very densely. (This is defined by APOT_STEPS in <tt>potfit.h</tt>)
+For analytic potentials this is not a problem, because the functions are sampled very densely. (This is defined by APOT_STEPS in ''defines.h'')
-<!--It is planned to implement different potential specifications, including potentials given by a functional expression, expansions in orthonormal functions or superpositions of elementary building blocks (e.g. Gaussians). These functions might be less prone to oscillations.-->
+<html><!--It is planned to implement different potential specifications, including potentials given by a functional expression, expansions in orthonormal functions or superpositions of elementary building blocks (e.g. Gaussians). These functions might be less prone to oscillations.--></html>
 ===== Transferability =====
@@ Line 23: / Line 25: @@
 ===== Experimental values as reference data =====
-''potfit'' does not use experimental data during force matching, the potentials are adapted exclusively to ab-initio data, which means they cannot exceed the first principles calculations in physical correctness. While in principle implementing the comparison to experimental values is straightforward, we decided against such an addition. For once, in quasicrystals there are no experimental values that can be calculated directly from the potentials, so determining them would considerably slow down the target function evaluation. Secondly, most of the experimental values depend on the exact structure of the system, which in most cases is not known beforehand due to fractional occupancies in the structure model. A better way to use experimental data is to test whether the newly generated potentials lead to structures that under MD simulation show the behavior known from experiment.
+//potfit// does not use experimental data during force matching, the potentials are adapted exclusively to ab-initio data, which means they cannot exceed the first principles calculations in physical correctness. While in principle implementing the comparison to experimental values is straightforward, we decided against such an addition. For once, in quasicrystals there are no experimental values that can be calculated directly from the potentials, so determining them would considerably slow down the target function evaluation. Secondly, most of the experimental values depend on the exact structure of the system, which in most cases is not known beforehand due to fractional occupancies in the structure model. A better way to use experimental data is to test whether the newly generated potentials lead to structures that under MD simulation show the behavior known from experiment.