C Force- and torque-free volume modulus

C.1 Global volume interaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 C.2 Comparison to other approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213 C.3 In-plane or out-of-plane volume forces . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 C.4 Search for the volume energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215

Let us analyse whether our implementation is force free. The relation (3.7) can be rewritten using the fact that

nABC = (B−A)× (C−A)

2SABC .