diff --git a/src/geometry/backbone.py b/src/geometry/backbone.py
new file mode 100644
index 0000000..75b08a3
--- /dev/null
+++ b/src/geometry/backbone.py
@@ -0,0 +1,13 @@
+
+# Ideal geometry. Angstroms for lengths, degrees for angles.
+GEO = {
+    'N_CA_len': 1.46,
+    'CA_C_len': 1.51,
+    'C_N_len':  1.33, 
+    'N_H_len':  1.01,  
+
+    'N_CA_C_angle': 111.0,
+    'CA_C_N_angle': 116.0, 
+    'C_N_CA_angle': 122.0,
+    'C_N_H_angle': 119.0, 
+}