Fix sign error in Schiller force model

7 jobs for schiller in 15 minutes and 31 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #448052
cuda11 docker
build-documentation

00:00:41

passed #448051
cuda11 docker
flake8-lint

00:00:07

passed #448049
docker
minimal-conda

00:01:27

passed #448047
win
minimal-windows

00:02:25

manual #448050
AVX cuda11 docker allowed to fail manual
pycodegen-integration
passed #448046
AVX cuda11 docker
tests-and-coverage

00:06:16

89.81%
passed #448048
cuda11 docker
ubuntu

00:15:29