# [lammps-users] Thermal Conductivity for Cu cutting using Reverse NEMD

Dear Mayank,

Hi,
I read all the papers relating to Reverse NEMD and found that this algorithm is used only for "fluids" can this >algorithm can be used for solids such as Copper. Because after momentum swaps the system responds to >non equilibrium situation by letting momentum flow in opposite direction via friction. Will this be a case in >solids. Also, can I still use fix thermal/conductivity?

I have used the thermal conductivity fix to measure the thermal conductivity for Cu and Ag EAM potentials (cuu3.eam, aguu3.eam). MD underestimates the values for thermal conductivity. This is because MD simulates the phonons contribution to heat. Thermal conduction in solid materials takes place by the contribution of both the vibrational energy within the lattice (phonons) and the free electrons. Free electrons are the
major contributors especially at low temperatures to thermal conductivity. Please read the paper by "P Heino and E Ristolainen. Thermal conduction at the nanoscale in some metals by md. Microelectronics Journal, 34:773–777, May 2003." to get more details.

Heino proved that there is a size dependency of the thermal conductivity k. Considering their curves of thermal conductivity against domain size we get values of 4.6W/mK and 2.3W/mK for Cu and Ag respectively, for my domain size of y=16 nm. These values are unrealistically small compared to experimental values which are 397W/mK and 420W/mK for Cu and Ag respectively.

Using the fix_thermalConductivity for my system the thermal conductivities for Cu and Ag were calculated to be 3.26 and 2.18W/Km respectively, which is in a good agreement with Heino’s work.

Regards,

Nicholas