<div dir="ltr"><span style="font-size: 10pt; font-family: Arial, sans-serif; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">Dear cp2k users and developers,<o:p></o:p> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">I am testing a NVE simulation with velocity scaling for crystalline CaO (300 K) and having questions regarding the drift of center of mass.<o:p></o:p> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">In a regular NVE simulation, I am expecting that (1) the simulation box is fixed and positions of atoms can be in fractional/scaled or Cartesian units, (2) if atoms moved out of the simulation box, they can be folded back to the box or left unchanged, (3) the mass-averaged position centers oscillate around x, y, z direction. I am showing the center of mass positions from VASP, which are consistent with the expectation.<o:p></o:p><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <a imageanchor="1" href="https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s1600/cp2k-vs-VASP.TIF" style="margin-left: 1em; margin-right: 1em;"><img src="https://lh3.googleusercontent.com/-tRDdhXVYalE/WGxP2ScXNBI/AAAAAAAAhnk/8bGLtoxRwxINxHoXywkIJFBPOkR4IipMwCLcB/s400/cp2k-vs-VASP.TIF" border="0" width="400" height="170"></a><p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">If I do the same for cp2k (input file enclosed), I am clearly seeing drift of center of mass. If I analyze the dynamics of the trajectory (now shown), it appears that both Ca and O atoms are diffusing instead of vibrating, as obtained from VASP trajectory.<o:p></o:p> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">I am wondering if you have seen similar behaviors or if I have the wrong settings in the input file.<o:p></o:p> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;"> <p class="MsoNormal" style="margin-bottom: 0.0001pt; line-height: normal; background-image: initial; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial;">Thanks, Wei<o:p></o:p></div>