Differences

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--- potfiles:format0 [2018/09/23 10:23] – daniel
+++ potfiles:format0 [2021/03/29 21:08] (current) – daniel
@@ Line 1: / Line 1: @@
 ~~NOTOC~~
 ======  Potential File Format 0  ======
 -----
+===== Format specification =====
 The potential format ''0'' is used for analytical potentials exclusively.
@@ Line 18: / Line 21: @@
 === type ===
-The ''type'' keyword has to be followed by the [[:analytic_functions|unique identifier]] for
+The ''type'' keyword has to be followed by the [[models:analytic_functions|unique identifier]] for
 the analytic function. To enable the smooth cutoff option ''_sc'' can be added at the end of the identifer (this also adds another parameter to the end potential function!).
@@ Line 30: / Line 33: @@
 # Lennard-Jones with smooth cutoff option enabled
-type morse_sc
+type lj_sc
 epsilon 1 0 2
 sigma 1 0 2
 h 1 0 2
 </code>
+All list of all supported analytic potential functions is available [[models:analytic_functions|here]].
 === cutoff ===
@@ Line 52: / Line 57: @@
 with an identifier for that parameter followed by the starting value, the minimum and maximum value for
 that parameter. The order of these parameters is fixed, for the implemented analytic functions the order
-can be found [[:analytic_functions|here]].
+can be found [[models:analytic_functions|here]].
+Giving three times the same value will remove this parameter from the optimization table and use exactly that value when calculating forces/energies. This is usually called a fixed parameter.
+----
+===== Additional features =====
+====  Global parameters  ====
+//potfit// supports global parameters, which can occur in different potentials. With this feature it is possible for any potential to "share" parameters with each other.
+To use them, you need a section starting with ''global <n>'' after the header in your potential file, where ''n'' is the number of global parameters.
+The format for the parameters is the same as for normal parameters: ''name value min max''.
+If you want to use a global parameter in a potential, use the name of the global parameter and add an exclamation mark.
+<code potfit>
+#F 0 3
+#C Mg Zn
+#I 0 0 0
+#E
+global 2
+glob1 1 0 2
+glob2 2 0 5
+type lj
+cutoff 8
+glob1!
+glob2!
+type lj
+cutoff 8
+glob2!
+glob1!
+</code>
+====  Smooth Cutoff  ====
+The smooth cutoff function is very important for analytic potentials since it ensures that the
+potential and its gradient vanish at the desired cutoff radius.
+Therefore the potential is multiplied with a cutoff function $\Psi$.
+$$V_{SC}(r)=\Psi\left(\frac{r-r_c}{h}\right)V(r)\qquad\text{where}\qquad\Psi(x)=\frac{x^4}{1+x^4}$$
+To enable the smooth cutoff for a potential, ''_sc'' has to be added to the potential identifier.
+<code potfit>
+type lj_sc
+cutoff 7
+epsilon 0.1 0 1
+sigma 2.5 1 4
+h 1 0 2
+</code>
+Potentials fitted with the ''_sc'' option will have an additional parameter ''h'' at the end.
+If you omit it, it will be kept fixed at a value of 1.
+----
+===== Examples =====
+<code potfit format_0_example.txt>
+#F 0 1
+#C Al
+## Al-Al
+#E
+type lj_sc
+cutoff 7.000000
+# rmin 2.159655
+epsilon 2100.0633799282 0.500000 10000.000000
+sigma 10.3066290006 1.000000 20.000000
+h 1 0.5 2
+</code>
+Many more examples are available in the [[examples:potentials|potential examples]] section.
-A sample format 0 potential file for a binary system with an EAM potential is available
-{{:format_0.pot.txt|here}}.