## 1 Introduction
The evaluation of the mass accommodation coefficient by either of the ratios given in Equation (1) or (2) requires the knowledge on the spontaneous  
Figure 1: Phase equilibria simulation scheme with denoted interface region boundary positions and mass fluxes through the interfaces. The density profile for the scheme was obtained from the production run of the liquid-vapor phase equilibria simulation. evaporation mass flux (or for simplicity, the spontaneous evaporation rate) \(J_{sp}\) for the liquid surface conditions, at which the rates \(J_{out}\) and \(J_{col}\) are measured. The spontaneous evaporation process is independent of the vapor phase conditions that the liquid surface is in contact with (or if the liquid is not in contact with the vapor phase), and the process rate is a function of the liquid surface temperature only [24]. The spontaneous evaporation rate \(J_{sp}\) is estimated from virtual vacuum simulations, in which the vacuum condition is achieved at an arbitrary distance away from the liquid film surface by removing the evaporated atoms from the simulations. To compensate for energy loss due to evaporation, the temperature in vacuum simulations is typically maintained with a thermostat applied to the liquid phase without affecting the dynamics or the energetic characteristics of evaporating atoms at the interface [24; 26; 27; 28; 29]. However, with such a simulation temperature control approach, a non-uniform convex temperature profile across the liquid film is expected since the thermostat maintains the average desired temperature of the thermostat region inside the liquid film, while the energy is being drawn from the left- and right-side liquid surfaces due to the evaporation. Consequently, the surface temperatures in virtual vacuum simulations, which are performed to determine the spontaneous evaporation rate at a specific surface temperature, can be lower than the surface temperatures in phase equilibria simulations, in which the mass fluxes \(J_{out}\) and \(J_{col}\) are evaluated. Thus, the existing temperature difference can introduce errors to the mass accommodation coefficient evaluation using the molecular dynamics simulations. Furthermore, it is worth mentioning that the simulations, in which net evaporation takes place, including vacuum simulations, in general have a major drawback because of the depleting liquid film and a non-steady system state during the evaporation process, which leads to a limited amount of statistical data that can be gathered to capture the transient system state in short time periods, in which the system state can be considered as quasi-steady [30]. Therefore, it is difficult to obtain a high resolution of the properties of interest of the system (such as the temperature jumps at the interface), especially near the vapor boundary, where atom density is low. To overcome the mentioned problems, we propose a novel simulation approach, which allows one to capture the steady-state evaporation into virtual vacuum state by maintaining a constant number of atoms within the liquid film during the simulations. Since no previous studies investigated the alternative temperature control strategy to the standard technique, which leads to problematic temperature profiles and surface temperatures, we employ the proposed vacuum simulation approach for the case of argon at a temperature of 90 K to demonstrate how the alternative temperature control approach can flatten out the non-uniform temperature profiles across the liquid phase and influence the liquid surface temperature, which is desired to be the same as in the phase equilibria simulations to mimic the same surface conditions for spontaneous evaporation rate \(J_{sp}\) evaluation.