Merge remote-tracking branch 'origin/v2.4' into v2.4

regtest/crystallization/rt-sean-marks/Makefile

+include ../../scripts/test.make

regtest/crystallization/rt-sean-marks/bias_lambdav_plumed.out.reference

+#! FIELDS time lambdav restraint.bias
+ 0.000000   7.2076 22496.0626
+ 1.000000   6.9494 20797.1547
+ 2.000000   6.2397 16472.0541
+ 3.000000   7.4545 24182.1899
+ 4.000000   7.3494 23457.2582
+ 5.000000   9.0622 36655.3527
+ 6.000000   7.0511 21458.5391
+ 7.000000   7.5659 24963.3722
+ 8.000000   7.7447 26243.0367
+ 9.000000   9.5849 41268.1005
+ 10.000000   6.9599 20865.1878
+ 11.000000   7.0417 21397.1589
+ 12.000000   6.7326 19422.9449
+ 13.000000   5.9536 14870.6966
+ 14.000000   6.8506 20165.1815
+ 15.000000   7.4636 24245.7184
+ 16.000000   6.5030 18018.1170
+ 17.000000   7.2774 22966.6045
+ 18.000000   6.6827 19112.7819
+ 19.000000   6.9182 20596.5588
+ 20.000000   7.3312 23332.7696

regtest/crystallization/rt-sean-marks/config

+type=driver
+plumed_modules=crystallization
+arg="--timestep 0.002 --trajectory-stride 500 --dump-forces forces_bias_lambdav.out --mf_xtc some_frames.xtc"

regtest/crystallization/rt-sean-marks/plumed.dat

+# Water oxygens: atoms 1-N with stride 4 (TIP4P geometry)
+ow: GROUP ATOMS=1-16500:4
+
+# Fixed virtual atom which serves as the probe volume's center (pos. in nm)
+center: FIXEDATOM AT=2.5,2.5,2.5
+
+# Calculates q_{l,m}(i)
+q6: Q6 SPECIES=ow SWITCH={GAUSSIAN D_0=0.32 R_0=0.01 D_MAX=0.34} LOWMEM
+
+# Calculates Lechner & Dellago's \bar{q}_{l,m}(i)
+qbar6: LOCAL_AVERAGE SPECIES=q6 SWITCH={GAUSSIAN D_0=0.32 R_0=0.01 D_MAX=0.34} LOWMEM
+
+# Probe volume
+sphere: INSPHERE ATOM=center DATA=qbar6 RADIUS={GAUSSIAN D_0=0.5 R_0=0.01 D_MAX=0.52} SUM LOWMEM
+
+# Renormalize
+lambdav: COMBINE ARG=sphere.sum COEFFICIENTS=1.732125 PARAMETERS=0.0 POWERS=1.0 PERIODIC=NO
+
+# Bias the mean value of the OP in the sphere
+restraint: RESTRAINT ARG=lambdav AT=0.5 KAPPA=1000.0 SLOPE=0.0
+
+print: PRINT ARG=lambdav,restraint.bias FILE=bias_lambdav_plumed.out FMT=%8.4f