Update document

doc/command-options.md

@@ -903,6 +903,9 @@ file, where $A_{\mathrm{q}j}$ is normalied as given above, i.e., numerical
 sum of stored value for each band should become roughly 1.
 ```
 
+An example of application of spectral function calculation is found at
+{ref}`spectral_function_reference`.
+
 (jdos_option)=
 
 ## Joint density of states (JDOS) and weighted-JDOS

doc/index.md

@@ -58,6 +58,7 @@ phono3py-api
 phono3py-load
 tips
 citation
+reference
 changelog
 ```
 

doc/reference.md

@@ -0,0 +1,12 @@
+# References
+
+(spectral_function_reference)=
+## Self-energy, spectral function, joint-density of states
+
+“LO-mode phonon of KCl and NaCl at 300 K by inelastic x-ray scattering
+measurements and first principles calculations” Atsushi Togo, Hiroyuki Hayashi,
+Terumasa Tadano, Satoshi Tsutsui, Isao Tanaka, J. Phys.: Condens. Matter 34,
+365401-1-15 (2022) [[doi]](https://doi.org/10.1088/1361-648X/ac7b01).
+
+
+